I do not see opposed checks being in the game. How would you handle an opposed check situation? For example: Trying to close a door on a bunch of living dead who are banging on it or trying to trick the zombies to distract them.

Would you just simply do a regular check or would you handle it as an opposed roll for these kinds of situations?

Well it would be a conflict (pg34). There are rules for opposed tests (pg20) as well.

One thing I did for my players, I had them run into other survivors, one of which was bitten and bleeding out. the NPCs wanted to take him to the hospital, but my PCs didnt want them too (they had a bunch of supplies in their truck, and wanted to run away from civilization). So I had one of the PCs and an NPC get into an argument and they rolled Charisma tests. Whoever got more successes = persuading the other to their point of view.

As for zombies banging on the door, you could make it an opposed test, that would make the situation more tense. It would be easier though to just do a direct test with quite a few negative dice.