To record your guitar in GarageBand, follow these steps: 1. Connect your guitar to your audio interface or computer's audio input port. 2. Open GarageBand and create a new audio track. 3. Select the input source for the track as your audio interface or computer's audio input. 4. Arm the track for recording. 5. Press the record button to start recording. You can now play your guitar and GarageBand will capture the sound.