For each kill, you will be rewarded with XP that can then be used up to rank up. The game is offering you 5 different maps with a functioning day/night cycle.
That’s important because you get awarded with more XP points during the night. When it comes to weapons, these will be scattered randomly around you.
Ammo will be limited, so you need to switch weapons frequently. You can also use your surroundings to eliminate your enemies. You can shoot a car tank so that it explodes and kills everyone around.