You can shorten both audio and MIDI regions so that only part of the region plays. You can lengthen MIDI regions to add silence to the beginning or end of the region. In addition, you can resize the common edge of two adjacent regions to control the transition between them.
In GarageBand on Mac, move the pointer over the lower-left or lower-right edge of the region.
When the Resize pointer appears, drag the region to shorten or lengthen it.
In GarageBand on Mac, move the pointer over the upper edge where two adjacent regions meet.
Note: If there is a gap between the regions, the Loop pointer is shown when you move the pointer over the upper-right corner of the earlier region.
When the Junction pointer appears, drag left or right.
Both regions are resized accordingly, with no gaps between them.