What is the homecoming dance anyways?

I'm a girl who got asked out to the hc dance, but I don't get what the homecoming dance is anyways,....I heard that they're suppose to be traditions and all...like something about mums...and well...CAN ANYONE PLEASE tell me about these traditions?? Especially about the mum thing....like I mean are the guys suppse to give it corsages to girls...and vice versa excpet with garters??? please? anyone?