Wounds can heal just fine whether covered up or uncovered but allowing the wound to get some air will usually speed up the healing process.
Your body naturally forms a scab over the wound when it's beginning to heal to protect the wound from infection so when the scab comes off the wound then the wound is fully healed by then.
You can however cover the wound with some petroleum jelly or Vaseline to keep the wound moist and promote healing and the Vaseline or Petroleum Jelly will keep a scab from forming but also protect the wound from infection.
Of course though if the wound is bleeding you need to either put a bandage on it or get stitches on it but if it's just a small wound that is not bleeding or has stopped bleeding then you can either leave it uncovered or cover it up.