As time goes by, both with use and with dying, your armor and weapons will both suffer damage, there is a minimum condition noted on each piece of armor or weapons you have.
You will see a bar showing damage, and when an item is close to being below minimum condition it will turn red.
To repair an item.
- Purchase a repair kit from a merchant or have a repair kit crafted for you
- Make sure it’s the correct repair kit (ballistics for guns/rifles) (armor for armor) (weapon for melee weapons)
- Press the "G" key and right click the item to repair
- Scroll down to the repair option and click on repair