A crankbait is a hard-plastic minnow imitation built around a plastic or polycarbonate lip. The lip does two jobs: it forces the bait to dive on retrieve (deeper lip = deeper dive), and it sets the wobble — tight and fast for cold water, wide and lazy for warm.
Crankbaits are sized and shaped to dive to a specific depth, called the running depth. A "shallow crank" runs 2-6 feet, a "medium" 6-12, a "deep diver" 12-25+. Match the depth to the structure you're trying to bump — a crank that's pinging bottom or ticking rock is in the zone.
The hits are violent because a crank covers a lot of water and finds active fish. Use it as a search bait first; switch to a slower presentation once you've found a school.