Undefeated Points, or UPs, are earned by attending an Undefeated campaign session. Everyone who attends a session, including the DM, earns one UP.
UPs can be spent to unlock non-core-book classes, feats, items, races, and spells. Once something has been unlocked it is available to all players. The Current List of Unlocked Items page keeps track of what has been unlocked. The Current Undefeated Points Spent page keeps track of how many UPs each player has used.
In order to spend a UP a player must simply tell the DM what they intend to unlock along with its source. For example, if a player wishes to unlock the feat Improved Toughness they can simply e-mail the DM, state that the feat comes from the book “Complete Warrior”, and that it can be found on page 101 of that book. The DM will review it, decide if that feat fits with the campaign, and let you know whether or not if the feat is allowed.
Once something has been unlocked it is available to both you and anyone else playing in the campaign.