What happens when you crack your fingers?
Your knuckles pop.
Nothing really, it's just air bubbles in your joints popping.
you can be opening yourself up for joint trouble later in life if it becomes habitual and too frequent .
You can get severe arthritis when your older. I do it too though
Air gets trapped in the joint and pops as it is released. It doesn't really cause major problems.
The synovial fluid in your joint evaporates, keep doing it and your fingers become thick at joints which disfigures them