All other messages you type will be seen by everybody on that channel. Some chatrooms are private. This means you're the Channel Operator, and thereby the 'ruler' of this channel. It still is shown in the list of channels, but it is very difficult to find out who's in it. As user of a channel you can set your usermode.
Some chatrooms organize special events or meetings.
An arranged time to have a party, or a conference, or what ever the chanops seem fit. The IRC channels themselves, where you can also ask your questions. There is also the possibility to chat while being visible as a comic strip character. Microsoft Comic Chat is easy to use and a lot of fun, since you can change the expressions of your character. If you do, you can download that free as well.