1. Lootboxes
2. Crafting
3. Loot other players

Lootboxes can spawn randomly in the world and will respawn after a Player looted the chest. They have a chance to have diffrent stuff inside.

Crafting is the most effective way to get Guns. You can find out how to craft Guns here.

Loot other players after u killed them. The Loot is now yours.