Uh oh, I forgot my most important rule:
I always use the Pen Tool in Smart Mode. The default Pen Mode is for Bezier experts. It works great for them, but not for me! Smart Mode is the second choice listed across at the top when you click on the Pen Tool in the Tools Menu on the left. Every time you click it gives you a curving node. To get a sharp node, hold down Alt when you click. You can also select a curving node, then hold down Alt to get a sharp node.