To have an orgasm. The word 'rocks' can be compared to the testicles of the male, but the phrase also applies to females. See also bust a nut.
Man, that girl really gets my rocks off.
The first thing i had to do was finger myself and get my rocks off before i got any more stressed
reaching a sexual climax; sexual intercourse
I'm getting my rocks off with that man tonight.
I got my rocks off last night!