This was a pain for me to figure out but once I got it figured it, it was simple.

Use the line tool. Instead of clicking and then dragging—which will draw a single line—click at the start of your shape, then click on the next corner, and then the next corner, and so on until you’re done.

To close the shape, your final click should be on the starting point. You can customize with the fill tool—if you do, then when you close the shape, you’ll automatically get a color fill.

Use the curved-line selection for wavy edges, and the straight-line selection for nice, straight edges.

If you don’t close the shape, you end up with a multi-point or wavy line instead.

Here’s a video that shows you how to use the line tool with clear written instructions in the extended caption.

I should illustrate this with screenshots but I need to move on now. Maybe another time.