for a few stuck heres a few helpers in game to get you started.
when you get enough points you can upgrade gun at one of these vending machines
also you need to buy ammo which will be at a ammo box like this and cost 50
if you melee / use knife ten times depending on what class you are u get a special weapon

it could be a stillsaw a crossbow or something else.
what i would say is dont go rambo off round the map cause if they back up and you get swarmed your done for

stay with the group and try to heal people if its worth healing for the whole group. also in between normal rounds there are special rounds where you get special zombies like just zombie dogs or flaming zombies that are on fire .these rounds are normally very hard !
there are tweleve maps in rotation at moment which you vote on at end of each map to which you play. or you can just replay the map you just played. heres most of em
7th station, bunker, city,dust2, hammerjacks, isle, oasis, pyramid, school,street,vacant
just checking out few more maps see if there good and compatible