Click the Channel List button or menu choice. A dialog box appears, displaying a list of channels or a dialog box to narrow the search criteria. Click a button labeled Get List or type List in the text box to see a full list of the channel names. Select a channel name and click a button labeled Join or Connect. You can often simply double-click on a channel name. Congratulations, you've joined the channel!
When you join a channel, much of what goes on in IRC becomes immediately apparent. You see a list of nicknames for people on that channel, and you see their messages appearing. If there are many people talking, their comments may be quickly scrolling off your screen. It's clear to see who is saying what, because their nickname appears in front of each message.