As much as we love copy/pasting in our everyday life (job applications, school exams etc), it can be a bit exhausting pressing Ctrl/Cmd+V over and over again to have the same drum pattern for an entire song. Therefore, the existence of loops!
First, make sure you're in the Editor area and that you can see the region you'd like to loop. Then, click the loop icon in the upper right corner (1) and drag to the right and you'll see "shadow segments" of the region appearing. These mirror whatever is in the base segment (the original region), so if you change the base segment, the shadow segments will change accordingly. Let the looping begin!
Check out this video for a clearer view.
(1) loop icon