how do bhop?

Don't use W or S.
Use ONLY A and D.
EIther bind scroll down or up (or both) to jump, and jump as you're hitting the ground (not after), or find a server with Autobhop (or enable it yourself, google the console commands).
When holding A, look left smoothly and vice versa.

Going left an right repeatedly will help you gain speed if you're jumping instantaneously after hitting the ground.