Young rabbits can be hard to sex,go to a breeder, and they can show you how to tell the difference.You will be able to see the testis in an older buck.

On young rabbits you turn them over and gently push down on each side of their sex organ, In a male you should see a tiny tubular projection pop up and on a female there will be none. Easy, I used to raise rabbits, and I could always sex them this way as soon as I started handling them.

Yep...that's explained pretty good, and if someone shows you it's
even better.

Flip bunny over
using your index finger and middle finger, press down gently on either side of the genitalia opening until the genitals pop out. Donut is boy, Taco is girl.