It's rather simple. Basically you write out what your character does or says just like any other post, but you leave space for the other person's character to react to what your character does. You should never control another person's character without their permission.
So you don't want to type too much in a single post, lest you accidentally control the other RPers character.
yeah i am still interested. thanks for being willing to take me on as a mentee. i have not really done much roleplaying i have always preferred the vid games, but i have beaten all of them at least once, and with roleplaying, it can change up a lot, so i wanted to learn how to do this. i may not be on every day, i will be on most. i will try to alert you when i wont be on. thanks :)