Whatever you do, don't pour it into the gravity feed for the fresh water tank or you will have to do a lot of flushing to get it out. And there have been indications that the RV Antifreeze that's sold in some places, like WallyWorld contains ethyl alcohol and may cause damage to some of the plastic in the plumbing. Don't buy it, look for pure propylene glycol on the label. An RV parts store should have it.
Look through the resources that Dave mentioned and check back if you have questions. Let us know which model of trailer you have, and if possible, take a photo or two of the docking center where your water connections are. There are variations between different models.