Also it is ok to be able to crack your jaw?

Not necessarily. Popping or cracking is usually due to muscle imbalance or joint problems, though painless popping of joints can be harmless. It could cause problems if frequent. Isometric exercises that use resistance- tightening muscles without movement-are very helpful for preventing problem popping. Joint problems usually improve with this, but may need medical attention if it gets worse.
No. The cracking is the dislocation and recapture of the articular disc. It implies laxity of the ligaments holding it in place. Also, related to joint subluxation. You should not do, it. And perhaps, see a dentist trained in tmj.