Can someone explain the differences between Post Processing software?

Got it. I am not too keen on how the whole compression thing works.

Another stupid inexperienced question then. So I open up a jpeg photo in iPhoto and adjust the contrast a little. If I don't actually hit save, and just close or quit iPhoto is there any loss?

So what I'm understanding is that if I do a literal save, that is where the loss comes into play? And if so, for my use, why then would I do an actual save? When I just hit quit in iPhoto and then come back everything is saved even though I have not done an actual save.

I know I know. Please don't kill me. I'm just trying to understand all of this stuff. Not very good at it.

Thanks