Okay, so I have heard a lot of things about using unity free for commercial use. I heard that you can use unity free for commercial use but you have to buy unity pro after releasing it on steam or whatever. Or you cannot release game for commercial use or whatever blah blah. Here's an example. Let's say I made a game using Unity 5 free. Could I then put it on like steam or whatever and profit off of it?

You can use Unity Personal until you make revenue of 100K per year. That's all there is to it.

Yes, within the 100K limit, like BoredMormon described.