Confused at what these channels are? How to access them, rather than clicking them? Look here!
Control + W = World Chat (Entire server - or /w)
Control + R = Reply to whisper/tell (or /t name)
Control + P = Party Chat (or /p)
Control + A = Battlegrounds chat
Control + S = Say Chat (or /a)
Control + F = Looking for Party (LFP) chat (or Recruiting)
Control + Y = Map Chat (Same as LFP except on same map, and for bosses, assistance, etc)
You may also change the filters in your tab by right clicking on them and manually changing the settings.