Each map consists of 20 waves, each one adding more enemies. In essence this mode is very easy but you can die easily if you aren't careful or don't know the best strategy. If you die you respawn as long as you partner doesn't also die. Each map also has a set of weapons that unlock at wave 5, 10, and 15. These weapons must be purchased using "segments" of intel, and they are placed on the map and are shown to you when they are unlocked.
For the first map you will want to have one person camping inside the building at the top of the stairs inside and the other outside inside the shed to the left of the broken wall.
NOTE: These pictures were taken in Bodycount Mode so some things are missing from them.
The weapons that are unlocked on this map are:
Wave 5 - SUPER90
Wave 10 - G36
Wave 15 - MINIMI