When making an underarm service, you are supposed to face the net and the opponent's court, aiming towards the desired target area.

Here are the answers to your questions:

1. When making an underarm service, you are supposed to face the net and the opponent's court, aiming towards the desired target area.
2. The part of the arm that contacts the ball when hitting it during an underarm service is typically the heel of the hand or the flat part of the hand (sometimes a closed fist).
3. The single hand dig pass is useful in a game of volleyball when the ball is hit far away from the body or out of reach for a two-handed pass, often in an emergency defensive situation to keep the ball in play.
4. The underarm service is a basic volleyball serve where the player holds the ball in one hand, swings the other arm underneath the ball, and hits it with an open hand or fist to send it over the net. It is known for its control and is often taught to beginners.