Roleplay is when you act out scenes and lives.
Have you ever wanted to be a demigod? Have you ever wanted to be one of the 5 cohorts? What about the 12th legion? Or, have you ever wanted an immortal god as your parent? Working your way up from probatio to centurion takes hard work and determination, do you have what it takes to be at Camp Jupiter?
Fanfiction is when you write a story based on another story (in this case the Heroes of Olympus Series) but in mostly Roman view. You may have Greeks, etc in a story but try to keep it mostly Roman-like. You can use Roleplay characters in Fanfiction stories but don't have to. The best story gets rewards!