You can select one of GarageBand's amplifier combination effects to quickly get started playing with a specific type of sound. They incorporate a combination of amplifiers and stomp box pedals to produce different genres, sounds and effects.
With a new guitar track open and a guitar plugged into your interface, you can select a type of amplifier combination to play with.
Select a Combination
In the right sidebar, click on the Guitar Track bar's arrow.
Scroll through the list to select a sound for your track. The options include a variety of genres and effects to fit the specific sound you're looking for.
Change the Amplifier
If you like a combination's stomp box pedals but want to change just the amplifier, you can scroll through the amplifier options by clicking the arrows on either side. This will give your combination a new type of sound.