What does privation entis and privatio bonis refer to?
Privatio bonis seem to tell us that evil cannot exist. It is just nothing.
How then can we speak of "evil" as something that exists if it is just a an absence of "good"?
Privatio entis is more complicated as I couldn't find anything worth reading on it for a beginner.

Evil isn't non being simply speaking, but in a certain respect.

Privation means lack of something that ought to be there. Lack of sight is not a privation in a tree, but is in a man, since sight belongs to man. Hence blindness names an evil (physical, not moral) in a man or a dog, but we don't call a tree blind.

Likewise, we don't call the lack of some due order in the will evil in the isolate, but as a lack in the will. Hence the act itself becomes evil, due to the lack in the act, just as a bad man is bad due to the due moral ordering he lacks.

Lack in the act? What does that refer to?
And what does lack in the will refer to?
Please give me an example.

It refers to evil naming not something simply not existing, but as not existing where it should.

So a sinful act is evil because it is defective... It lacks an ordination to some good which ought to be there. Hence the analogy with blindness ...

So sinful act have both an ommission and commission?
But I don't see what Privatio Entis have to do with sin?