1) Buy a pick at your local hardware store
2) Use your nail and hold it in place in front of the lock
3) Use your pick and insert it into the lock. You should be able to push up and feel individual pins (most household doors have 5 or 6). Push each pin all the way up until it sets (you should hear a click) and continue to do so for all the pins.
4) After setting every pin, turn the pick with your nail and your door should be unlocked!