Ya man, at alot of parties there aint much dancing.
You asked "Is it really necessary", well of course NOT! You are supposed to dance to enjoy yourself. If you cant enjoy yourself when you are dancing, you are a fake, and will prolly look like a fag.
If ur gonna dance, try grinding behind a girl. Really sexual and its very common
Try to just "move your body" to the beat, DO NOT swing your arms like a ****ing monkey and run around the room. Do some cool stepping, move ur arms around in small movements near your body. Its rather simple.
Just enjoy yourself man! Dont stress about a party!
Remember, people stress at school from work or material, they go to parties to HAVE FUN, to get away from the stress and hard thinking. Half of em will prolly be too drunk or stoned to know wtf is going on
So once again, to sum it up: Do what you wanna do, dance how you wanna dance, and most importantly HAVE FUN