iChat lets you type messages or speak with others, but with broadband and a good computer you may also add video.
Make sure you’re online, view the Buddy List and then chat. Even send files through iChat.
The iChat Setup Assistant asks for your name, screen name, password and Account Type. Other Tips in this series give you more information too.
How to get a free Screen Name from AIM, so that you can set up iChat, to talk with friends all over the world.