The Plus Tool in GarageBand can perform many functions. In this tutorial, you will focus on splitting up parts of your audio wave in the track editor.
When you click, drag and highlight the audio region you're focusing on, you'll be allowed to perform a quick split of that region for the purpose of dissecting it very quickly.
First listen for the part you wish to dissect. Take note of where the beginning of that part lies on the timeline.
Staying below the audio wave so the cursor becomes a crosshair, click and drag the portion of the clip you wish to highlight. Once selected, click once on that portion to perform a quick split.
Do this again to select the rest of the verse part that you want to extend two measures.
Select the region you split off and the region you split from by holding Shift and drag those audio regions back two measures.Now, select only the region you split off and press Ctrl/Command+C to copy.
Place the marker at the end of the clip you just copied and press Ctrl/Command+V twice to paste the clip two times. This will extend your selected audio clip by two measures.