Skills usually cost multiple credits, depending on the skill and the skill level. The more strength a player has, the more damage they'll do. Strength is also required to use certain weapons and open certain doors. Strength is the most important thing to get when creating a combative weapons based player. The more health a player has, the more damage they can take.
Health is the second most important thing to get when creating a combative weapons based player.
The more mana a player has, the more skills they can use in succession. Certain skills require more mana than other skills. Skills cannot be used without enough mana. Mana is the most important thing to get when creating a magical player. All players start out with full energy.