These are required items in order to hunt and defeat opposition, whether it be mob or even another player. There are many different weapons at your disposal, doing varied damage and varing in cost. Though it boils down into two flavors of combat: melee and range. Both have special needs (must constantly repiar melee, need lots of ammo for ranged), but when used wisely can be a good companion in the heat of battle.
Some ranged weapons can have attachments to upgrade and boost their performance.