The gate is an upgradable feature of your campsite. Its primary purpose is to serve as a barrier to zombie attacks when you are in camp.
When you arrive at the camp, the gate will be broken. You must repair the gate in order for it to function. To do this, you must first craft the Hammer. Once you have crafted the Hammer, equip the Hammer, go to the gate, and Use the gate to begin the repairs.
After the gate is repaired, you can upgrade it once. This changes the appearance of the gate slightly, giving the cross-hatched section of the gate the appearance of being made of metal. In practical terms, the upgraded gate can take a lot more damage from a zombie before it is destroyed.
Security-wise, the gate is the most effective source of defense for your campsite, both in terms of resource costs and the benefit conferred. When a zombie approaches your camp to attack, the gate will prevent it from advancing any further. Zombie will then attack the gate until it is destroyed. While the zombie is attacking the gate, you can attack the zombie. The zombie's attacks will hit the gate, not you.
An upgraded gate improves the efficiency of the Punching Machine X-26, and vice-versa. The gate holds the zombies in place, allowing the X-26 the time to reset itself and punch again. The X-26 inflicts significant knock-back and damages the zombies, preserving the gate's durability. Nevertheless, if you are in camp and experience a zombie attack, it is not recommended that you leave your gate and X-26 unsupported.
Repairing the gate after it is destroyed by zombies will not cost you any additional resources.