You would start with doing /tp lobby

then, look for the Roleplay portal, go through that.

You should see a booth right in front of you. Click the NPC.

If he doesn't respond, two things may of happened:

1. You've been here too long (doubt it since you joined the forums today)

2. You are already in the tutorial quest. To get back to where you were in it, type /q show

 If you haven't done any other quests, that one should load.

worst case scenario is that you just don't do the tutorial quest. though all hope is not lost! The site has in depth guides on how to use the chat and how to RP.

Here is is for a reference: https://www.massivecraft.com/massivechat