Newbie, can someone please help with a setting?

Hello,
Im fairly new at photography and really enjoy learning. I have been asked to take some photos of the kids at prom tonight. (I live in a low income school district and my husband is a teacher there, so of course it's pro bono) I have a canon rebel xs that I really like. What setting would you recommend for the shots? Should I change my ISO ? Any help or suggestions would be greatly appreciated.
Thanks!!!:confused:

Do you have a 50mm lens? If so even the F2 version will give the angle of view (around that of a 75mm film lens) which was a favorite portrait lens length. It will give you the shallow DOF when opened and give you working distance. If you have lightening you may not have to use your flash. Make sure you have extra batteries and memory cards.

Thank you !!!! Yes, i have 4 lenses. It seems I lucked out and already had the lenses from another canon i owned!!!

You will want to up the ISO to the maximum noise free ISO setting if you are also take candid shots, and install the fastest lens you have, if you can keep the shutter speed above a hundred of a second you will have some good candid photos. You can always just use the noise at the maximum camera's ISO and convert to B&W and try to get the Tri-X film look for the candid photos. If you do not have studio light a couple halogen spots in the clip on fixtures for right and left lightening work fair for portraits.