Perhaps a better word than "moral certainty" is "practical certainty"--not better in an absolute sense, but better for discussing it with people who don't have a lot of philosophical training and are looking for easily accessible language to get a handle on things. For instance, Denise, you talk about being confident enough that a plane won't crash to ride on it even though you don't have absolute certainty. And that's a good illustration. Even if you've never ridden on a plane, you can be practically certain that it won't, practical in the sense that, shy of strong reasons to object to what is
usually true, you may as well treat this plane as if it's not going to crash.
So how do you get that degree of confidence? How can you say, for all practical purposes, "I know X," even if "know" here isn't exactly the same strength as knowing that 2+2=4 or that all triangles have three sides?
I actually think the approach is more pragmatic and straightforward than we most philosophers might want you to think--especially most modern philosophers. If you'll indulge me a bit of explanation, I'd start by pointing out the wrong approach. Descartes is the best example there is, I think. He's the one who said the famous, "I think, therefore I am." Here's a guy that, unlike you, wanted absolute certainty in anything and everything he claimed to know. His method, which I think was silly, and I hope you'll agree, was to doubt everything that could be doubted and only believe what was impossible to doubt. So you think the world is real? Maybe not! It could all be a dream! But at least I'm not a dream. Ah, but maybe I am. You've seen the Matrix. Maybe my body isn't real. Maybe some demon has my mind under a spell and I only think the world is real. Yada, yada.
Now there are answers to Descartes' method, but let's just ignore all the complicated stuff and just respond by rolling our eyes. You are right not to ask for absolute, perfect certainty that the plane won't crash, and you're right not to require that for mundane questions like, "Do I really exist?" and "Is the world a real place?"
In other words, let's just start with what is obvious--yourself and the things around you. That's the basis of all knowledge. The general principle is to start with the more obvious and think more deeply through to the less obvious. What must be true, or at least what is more likely to be true than not, based on what you already see and know to be true?
To cut straight to religious questions, let's ask that about Jesus. The first and most obvious thing is that there really was a guy named Jesus who existed. I know there are some skeptics who want to deny that, but remember there are always Descartes' asking you to prove the obvious, as if raising silly doubts about the obvious ("We might be living in a MATRIX!!!!1!1") is somehow good reason to think the obvious isn't really true. It's also obvious He got Himself crucified by Pilate, a Roman ruler, at the behest of the Jewish leadership. And while it's less obvious, it doesn't take much searching before you discover that it's incredibly obvious that just a few days later, all of His disciples were absolutely, 100% convinced that they saw Him raised physically from the dead. Anyway, I'm not going to do a full analysis of that type of argument, but those are the types of things you learn about Jesus pretty quickly. I'd encourage you to watch the video just below for a REALLY good explanation of how that argument works:
https://www.youtube.com/watch?v=ay_Db4RwZ_MSo let's step away from those type of arguments and come back to the present. Are you practically certain that God exists? If not, again, just look at things practically--don't be a Descartes. You see the world exists, so just ask the most famous philosophical question of all time: why is there something rather than nothing? Just imagine for a moment that there really was at one time absolutely nothing (side note: that question is grammatically meaningless, but I think you know what I mean). I mean take that seriously--there is just NOTHING. Then there is just something? And all of this? Out of nothing? How? That's just absurd. It's much easier just to recognize the obvious, practical fact that your senses have told you your whole life: nothing never produces something, and something always comes from something else. So the universe as a whole has to have come from something else, and what would you call that "something else" that caused the entire universe to exist? May as well call it God!
Well how do you know it's the CHRISTIAN God? Lots of ways, but I'd take you back to Jesus. If Jesus really did raise from the dead as very much seems to be the case, then it's probably better to believe Him on religious matters than not. In other words, if I believe what Jesus did (and if there is a God, as there seems to be, then no reason not to believe what He did), then I end up as some sort of Christian. By the way, the general existence of a God who cares about us is the virtual universal experience of all sorts of people, Christian or not. So, again, I just don't see how that's something that we practically argue against without becoming some silly Descartes.
So then what kind of Christian? Here's where I need to stop, because I obviously answer this question differently than the Catholics on this board, but I think the general rule still applies. I will say this much: we have the words of the earliest people who followed Jesus, and just as importantly, we have a lot of writings about
their very early followers. In other words, Paul had to get his ideas from somewhere; John, Peter, Jude, Luke, Peter, James, they had to get their ideas from somewhere. And the earliest Christians after them, people like Clement and Ignatius had to get
their ideas from somewhere. If you've already decided that Jesus is who He said He is and that the Christian God exists at least in some form, then those people matter a LOT. So ask yourself the practical question: is it more likely that those first Christians after the apostles--Clement and so on--got their ideas from the Apostles or that they made them up? If they got them from the Apostles, and the Apostles got them from Jesus, then that's a pretty strong and very practical argument for being Catholic. Now, full disclosure, I read history a little differently, but I think those questions still have to be answered fully and honestly.
Anyway, this post is entirely too long and I've not given many general principles--I'm mostly giving examples of how you think about questions related to Jesus, God, and the Church. But I hope you see the basic approach. You start with what is obvious. You avoid the temptation to ask for too much proof, to move the goalposts. You try to accept the world as it really presents itself to you. Then when you discover a new fact, you compare it to what you already know or what you think you know. If the new fact confirms what you already know, then great! And if it challenges or refutes what you already know, you ask yourself which observation has more to commend it--is the new fact so obviously true, or more obviously true than your old view, that you should adopt it and change your mind? Or is what you already believe based on ideas that are more obviously true than this new observation such that the new observation ought to be rejected?
And you spend your entire life like that, each day trying to learn a little more. If you conclude with the Catholics that Jesus really is God and that He really founded a Church and that Church really is the Catholic Church, then you can read what the Catholic Church says and take it with a lot of authority! That's why you'd be Catholic. And if you aren't sure about any of those things (if there is a God, if Jesus is God, if He founded a Church, if the Catholic Church is that Church), then you use the methodology I'm poorly describing here to decide if you think those things are, in fact, true.
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The alternative, by the way, to the above long process really is to just accept something by faith. If you do that, I would encourage you not to stay there but to take your faith and then start examining it and basing it on solid reasons. And either way, at some point, you'll realize that you've come to a place where you have more than enough reason to place your faith in something. At that point, you stop demanding proof and just say, Amen, deciding not to be a Descartes, just trust. So why would you just trust? Well look at people like PED and Obi, Jack3, and even the pickle, and others like them and decide if their experience (which is real!) and their own study and character is strong enough for you to say, "You know, I don't have all the answers, but they have more than I do, so I'm going to trust that as I study, I'll either get to where they are or find myself discovering the same answers they are." That's what we do when we're kids. We believe our parents. There's nothing wrong with that. Fr Obi is called "Father" for good reason, you know.
But in general, I'd say something like the above is how you know anything at all. You take what is obvious, what you can't deny, and you reason from there to what isn't so obvious but what is more likely true than not. You insist on not being a silly philosopher who wants absolute undoubtable proof for everything, and you just be realistic. It's amazing what you can find if you do that. Even better, I promise you from experience, it's even more amazing how much undoubtable truth you DO end up finding if you just let yourself have a little faith.
Sorry for the length of all this. God bless if you if you made it all the way through it. And if not, God bless you anyway! Merry Christmas.
might literally get the Book thrown at us... I have seen some nasty responses in my time.. 
