Was jousting a skill that was only used in exhibition? Or did knights actually engage in jousts on the field of battle?

If used in battle, why would they do that? Jousting as a tool of warfare seems very impractical to me.

Are there historical accounts of knights fighting to the death via joust? Was it a duel of part of some sort of larger engagement?

Bonus question: How did jousting develop? Was it a genuine tool of warfare that was augmented for exhibition or purely designed for entertainment?