This should open up the paragraph indentation bar that looks almost exactly like the one you get in other word processing software (Word etc). Right click on where you want your left paragraph indent to go (where your cursor moves to when you hit the tab key for the laymen like me). Now hit the tab key and your cursor will now indent a new paragraph exactly how you want it to.
I put this in first because every time I take a break from writing, or I use another piece of software for a while, then I usually forget how to indent my paragraphs once I get back into Scrivener. I end up firing my cursor across the page every time I hit tab. This can often turn my first writing session into a desperate Google trawl before I even get to start work again.