Ah, those wonderfull first steps into the world of RP...
I remeber mine from not so long ago.
RPing is just that: Playing a Role.
Make responses and act as your role (or character) would.
This can be as simple as commenting that your drycleaner's going to kill you after this zombie/sewer mission.
But it can also be as complex as you want it to be, for instance... hydrophobia (fear of water), which would make a sewer or cave mission a real nightmare...
Basicly, in it's simplest form, it's dropping game mechanics (XP, debt, that sort of things) and RL stuff from you (regular) chat. Other than Out Of Character (OOC) things like brb and afk or what not that helps the team (when on missions).
Most RPers I've met use double brackets (( )) to mark text as OOC, in order to avoid confusion.
I would also advice you to read this RP Guide
That should answer most of your questions.
If you have more, then just post them here, and someone will most likely give you an answer.
And lastly: have fun!
(I know RPing increased my fun in the game by a tenfold)
@ShadowGhost & @Ghostie
The Grav Mistress, Mistress of Gravity
If you have nothing useful to say, you have two choices: Say something useless or stay quiet.
Simply put, you're here to save the world and you're dressed up in Spandex.
No person in their right mind would chase into sewers filled with Zombies, so why are you doing it?
What's it smell like down there? Are you gonna be late for your girlfriend's anniversary?
Take an idea and run with it 
And most of all, have fun
right ive been playing coh since march and ive heard people talk about RP and stuff . . . . just i dont really kno the just of it . . . as in what is RP (not what RP stads for
) as in how do u RP and what is it about.
thx for help