It's actually not that complicated. Each match is a "day" of fighting for supplies. Each day, you have to acquire a certain amount of supplies that you naturally obtain through playing through the match; taking an enemy down, executing them, looting them, etc. If you meet this, your "faction" grows and maintains health. If it's under, you start getting sick people and eventually dead people. As your faction lasts longer and grows in size, you unlock more items.
Essentially it's regular shooter matches that also mesh into an individual's seperate little backstory.
