Apple GarageBand '09 - Manual (Page 59)

Chapter 6 Tutorial 4: Playing and Recording Software Instruments 59
To add a new Software Instrument track:
1 Click the Add Track button, or choose Track > New Track.
2 In the New Track dialog, click Software Instrument, then click Create.
A new Software Instrument track with a Grand Piano instrument appears in the
timeline, and the Track Info pane opens to the right of the timeline.
3 In the Track Info pane, select an instrument category from the list on the left, then
select an instrument from the list on the right.
The header of the Software Instrument track changes to the name of the instrument
you selected. If you have a USB or MIDI keyboard connected to your computer, you can
play notes and hear the Software Instrument right away. Even without a keyboard
connected, you can play Software Instruments with the Musical Typing keyboard or
onscreen keyboard.
Select an instrument
category from this list. Select an instrument
from this list.