Hey there! When you start an RP there are lots of things to keep in mind (story, how many characters, genre, ect) All kinds of crazy things. But since you're not sure where to start you could always just try a one on one RP first, and have the story be very loose, maybe not even have one.
Just try and find someone who will RP and maybe talk to them about what you want the RP to include, well planned RPs can be just as fun as ones that start out of the random!