My boyfriend is uncircumcised, and he said that our first time was painful for him because the skin hadn't ever been pulled back that far. Just be prepared and eventually it will get better. :)
If the skin is really tight, you can loosen it by gently stretching the skin outward each day. The opening can be expanded, so the foreskin will move over the penis during sex. This will take a while - perhaps a few weeks, perhaps months - so in the meantime, use lube during sex.
IM A WOMAN BUT I HEARD MY EX HUSBAND SAY IT IS HELL THE FIRST TIME AND ITS GONNA HURT ...