Hi meghan, I'm new here myself the super super simple explianation is some clever people use lots of maths and computers to create a virtual currency (cryptocurrency in tech speak) called steam dollars (it has real value). when you use the site to create content, comment or upvote you are helping create that currency, so the give you some of the steamdollars which you can later convert to cash. there is actually a lot more to it than that but I'm sure someone who knows it all better than i do will be along with some handy links soon.