You have a couple of derived stats that are used throughout the game. They are as follows: Guard, Spell Resistance, Toughness, Mana and Stamina.
Guard is your ability to avoid getting hit in combat.
Spell Resistance is your ability to shrug off spells and magical effects.
Toughness is a pool that represents your tenacity and ability to fight through pain before you collapse.
Toughness Pool = 14+Athletics+Endurance Ranks.
If your Toughness pool reaches 0, you fall unconscient.
Mana is a pool of magical energy that you can draw on to cast spells.
Mana Pool = 4+Cunning+Will Ranks.
If your Mana Pool reaches 0, you suffer a drawback (gotta find something to call it, and what it does)
Stamina is a pool of physical endurance that is used to exert oneself.
Stamina Pool = 4+Endurance+Will Ranks.
If your Stamina Pool reaches 0, you suffer from Exhaustion. (doesn't do anything yet)
Later in the game, you will gain more XP, and this can be used to buy new ranks and talents as you see fit. They use the same costing as used during character creation.