There are a few types of chat windows in your SWG Interface, each with its own function. Most system messages and /tell messages will appear in Spatial, but you can customize this. In order to customise what shows in the window of of your choice, double click the title of the tab.
Spatial[]
This is what you can see/hear in your character's immediate area. You can see what people whisper up close, or yell nearby.
Combat[]
All of the activity that occurs in combat such as damage taken and abilities executed.
Planet[]
Anyone on the planet you are currently on can chat in this window
Auction[]
Reserved for players wanting to sell/buy items.
GuildChat[]
The private chat of your Guild/Player Association.
GroupChat[]
Private chat with the other players of your current group.