You need 5 posts before you can chat I think, so go and make some random posts here and there first. Then click on chat and the box should open, type in the small box and then hit the button next to it. If you are typing but cannot see it you may need to change your font etc. For that go to your CP, in the tool bar at the top left, from there you can alter settings.
Ask away if you need help. I am assuming that you are a gymnast or teenager, the gang in the gymnast forum are really cool and very helpful, they are also the people you are most likely to find in chat.