1. Service Ace. If you score points off of an ace, I would consider this as a successful attack.
2. Kill. A non-returnable hit by a player.
3. Block. You can score points from successful blocks, but you likely shouldn't depend on blocks to score points.
4. Opponent Error. Scoring points off of opponent errors is definitely common at lower levels of volleyball. Focusing on making your opponent make errors is good strategy for winning.