How does renter's insurance work?

I had to have it in the last few places I lived. (and currently do) But I never really used it. I know that like if someone steals something out of my car it's replaced because my car is an extension of my property, but other than that, how does it work? Repairs? To help with getting my deposit back when I move? If there is something wrong I notice after doing the initial walk through? I have USAA if that helps with the answers?