What is the right use of bake and broil?
When you use an oven to bake, you can control it's temperature. When you use it to broil, it just turns on the element as high as it can go.

For baking or roasting, it is vitally important to control temperature, so don't ever broil.

When doing some veggies or meats (steaks, fish), you may want to broil. It cooks from the outside VERY quickly, so it is good for rare steak and partially cooked veg.