A role playing forum is a site where people who are interested in a plotline get together and write posts in a free style manner, each person controlling only their own character, and the characters interacting with each other much in the way that people interact in real life. For example, a popular role-playing type of site would be a Harry Potter one... People might all assume a Harry Potter character, and then could go into different "rooms" at Hogwarts and interact with each other.
The best way to learn about a role-playing forum, quite frankly, is to experience it. I recommend the following site, which is fairly easy to join into and isn't overwhelmingly large. The admins there are really friendly and can help you figure out what you're doing. This particular one is just based on being in high school....
http://www.forumer.com/ is a free website to host forums on, and after doing so you can customize it to fit the style of a roleplaying forum you like.
There are a lot of different ways and places to roleplay. 1) Forum-Based roleplaying, aka post-by-post or play-by-play roleplaying. Involves posting messages on a forum back and forth to develop characters through action and dialogue. Examples of forum software include InvisionPowerBoard and its other free boards, such as Zetaboards and Invisionfree. vBulletin, SMF, Proboards, phpBB, myBB and Yuku are other examples. However, changes to Proboards' recent policies make it an unsuitable place for roleplaying. 2) Text-based MU*'s, including MUDs, MUCKs and MUSHes. A MUD is a Multi User Dungeon, for example. I don't know much about these! 3) Chat-based roleplaying. This may be done over any instant messenger, such as AIM, Y!M, MSN, etc. Other options are ICQ, IRC or a chat client. You roleplay with another partner or multiple partners via the chat client. 4) Email-based roleplaying. You trade emails and roleplay back and forth with replies. Similar to forum-based roleplaying. These usually have a group, such as a Yahoo or Google group with information and contacts. I have personally roleplayed forum and chat, usually with chat supporting my forum roleplaying.
Go to the boards and it's under roleplaying.
There's a heavily filtered roleplaying forum on moshimonsters.com. Some kids roleplay on sites like Animal Jam and Toontown, but they aren't as active. There's a good roleplay forum on kidzworld.com.
The Metabarons Roleplaying Game happened in 2001.
Pathfinder Roleplaying Game happened in 2009-08.
Marvel Universe Roleplaying Game happened in 2003.
DC Universe Roleplaying Game happened in 1999.
The Lord of the Rings Roleplaying Game happened in 2002.
Amber Diceless Roleplaying Game happened in 1991.
Google 'warriors roleplaying' or go to www.freewebs.com and make your own warriors roleplaying website. Or, if you're really an overacheiver, learn HTML and make your own website.
Star Trek Roleplaying Game - Decipher - happened in 2002.