Q: Whats this 'exp bar'?
A: This bar denotes your current exp level, if it reaches a certain level you will be promoted to a post, here is some promotion level status

3000 level : Special Member
5000 level : Moderator(of a specific section)
8000 level : Forum Moderator
9000 level : Global Moderator (Team)
10000 level: Administartor


Q: How to use the chat box at the bottom of the main page?
A: Check the images this will help you in this problem