Hello. Welcome to cruise-chat. I use them all the time. I buy them either at Kmart or Walmart. You put your clothes in them, roll up the bag, and it squeezes the air out of a vent in the bag. I try to pack clothes, that don't wrinkle to bad. You can really pack alot more clothes using them. So, be careful of your weight limit. Be careful not to over fill the bag. Good luck, Lil' Lori