It's nearly impossible to tell which rabbit is male or female by just looking their physical appearance. The only way to determine their sex is to see their sex organs. Sexing a baby rabbit (under 4 weeks old) is harder to be done. However it's possible once you know the difference between male and female sex organs.
This is male
This is female
Older male rabbits (9 weeks old and above) is easy to determined as they've testicles. Sometimes the fur will always hide the testicles, so you should pushing the fur out and feel it with your hand.
Testicles of male rabbit
Sometimes it's quite tricky to determine the sex of your rabbit. The easiest way is to ask a breeder which is male and female rabbit. If they don't know then you should do it yourself!