How to generate profit from a startup

Night people, I'd like to understand better how is that someone generate a profit from a new web company, I'd like to know links an ideas from people with experience in this area.

I've try to think about this but I don't get it yet, I see a lot of new startups appearing every day and people financing them, but can't get how those are going to generate a profit.

I go to their sites to see what they do, the about sections, etc with little to no clue at all on how they think the idea will in someway generate something profitable enough to keep them running without spending the money given by investors or angels.