This means coop campaign, not the be the zombie game mode. Have one or more friends join your game and sometimes a message will pop up indicating a competition can be done, all players in the game have to accept before it begins. The winner of the competition gets XP in what ever category the competition falls under (survivor, Agility, Power) However on some competitions, such as races, there can be a draw. Everyone will get the XP but it will not count as a win for anyone, and if no one completes the competition its a loss for everyone. The competitions include...
Racing to a certain area (this will usually pop up if you put a waypoint on the map and then exit the pause menu, try not to do to much parkour as the climbing animation can slow you down sometimes. If you have the agility skill to vault over zombies, be sure to use that, but be careful not to spam it as that really kills your stamina.)
Collecting the most loot in the area (just spam holding down the
button while running around and don't waste your time picking locks, looting already dead zombies can be good).
Killing the most zombies in a certain area (if you have a molotov or so, just throw it at a group of nearby zombies and this will be a breeze, its always good to carry them with you in this game).
clearing out a safe zone (This is very similar to killing the most zombies but if there is a Goon (big zombie) inside the zone, let your buddies deal with him while you quickly pick of the little guys).
Inflicting damage to a Goon ( A goon can technically be any type of special zombie however its typical a big guy with a heavy rebar. If its anything besides a big guy then just go super aggressive on it and do as much damage as possible as quick as possible, if it is a big guy then using the first agility skill you unlock (Dodge) run up to him and hit him two or three times, when he tries to swing at you, use
to quickly dash away. Just run right up to him again and repeat).
Doing a certain mission objective (This is probably the most common one, besides looting. This can be any of the above Competitions, whether it be get to the objective the fastest, kill the most enemies etc. Just follow the tips above for each of them.)
Good Night and Good Luck