Please help me out here! I'm very inexperienced...

does a woman need to come before sexual intercourse, and if so, how does she know when she reaches peak?

As a man I think no, a woman does not need to come before sexual intercourse, but CAN. If she comes easily. The normal is that when she comes after 10-20 min intercourse. And how does she know? If she feels the need for squealing?

OMG DON'T listen to that!! ^^^^^^ yes it is possible to come before having sex. Through clitoral stimulation, oral sex or fingering you can easily come. Everyone's org**m is different. Some women get tingly everywhere and get a rush that lasts for a few seconds, some start shaking a bit, many have uncontrolable back arching, it is different, but you will definately know when it happens.