Its sort of complicated.
You start off with medpacks on a table. you grab those and then choose between two weapons. An UZI or a Shotgun. In addition to whichever you pick, you have a pistol with unlimited ammo.
Later on you can get and an automatic shotgun, an m16 type gun, or a hunting rifle (sniper basically). Along with a second pistol to duel wield.theirs also Molotovs that create fire, and pipe bombs
The game is pretty fricken sweet. If you play online you can be the infected (zombies) and you play either Smoker, Boomer or Hunter.
Hunter=Jump on people and rip them to shreds
Smoker=Zombie sniper, hang them from buildings with your tongue or drag them away from the group
Boomer= The puker/blinder basically. They mark the survivors with a bile that makes all the infected attack them!
I would really recommend checkin the game out!