In fewer words: you just need to shop around. Stick to group rps (1x1 section won't help you with this, and even experienced rpers have a hard time in there), read interest checks when you see them, join a few! Some you'll like, some you won't, and you'll learn as you go. You'll probably find yourself gravitating to fandoms and themes you already like from books, shows and movies, and you'll develop from there.