What is the difference between Bake and Broil in an oven?

you BAKE in an oven you broil on the oven top :it a process like boiling food in water unless of cause you mean BRAISE which is done in the oven near the top grill

Baking food involves heating the air around the food in order to cook it from the outside-in (since when you bake bread for example, the outside crusts, while the inside becomes soft and flakey).
Broiling food involves heating the food using infrared radiation. This method allows the food to cook evenly all the way through.

This is why you pre-heat the oven when baking, because the air inside needs to heat up, where as with the broiler, since it cooks evenly, the food can heat up while the oven heats up too.