Press Cmd+T (Ctrl+T) to select the Horizontal Type tool. (Repeat this shortcut to toggle between the Horizontal Type tool and the Vertical Type tool).
Click anywhere in the Comp window and start typing.
When you finish, press the Enter key on the numeric keypad to exit typing mode. Note that pressing Return (Enter) on the main keyboard won't finalize your type. Instead, it will drop your type cursor down to the next line, just like in a word processor. If you're working on a laptop without a numeric keypad, you can finalize your type by clicking anywhere outside the Comp window (i.e., the Timeline) or selecting another tool (i.e., the Selection tool).
After Effects will create a Type Layer to hold all your text. This is a new type of layer added in AE 6.0. The type layer will be automatically named after the text you type. (If you type "Hello," the layer will be named "Hello.") You can change its name the same way you'd change any layer name: by selecting the layer name in the Timeline and pressing Return (Enter) and inserting the new name .