When I was in high school, I would constantly hear about players using some sort of equipment that shocked their legs and made them jump higher. Does anyone know how it’s done and if it is safe? Thanks

No, don't believe this nonsense. If it sounds too good to be true, it almost always is.

Here are some proven ways to jump higher:

https://www.breakthroughbasketball.com/fitness/increase-vertical-jump.html

https://www.breakthroughbasketball.com/fitness/jump-higher.html