GarageBand for Mac: Enable tracks for recording
You can use a track’s Record Enable button to enable the track for recording. The Record Enable buttons include a circle that lights red when the track is record-enabled.
If the Record Enable buttons are not visible, you can configure the track headers to show them.
Enable a track for recording
Click the Record Enable button in the track header.
Click the Record Enable button again to disable the track for recording.
You can enable multiple tracks for recording.