Action points are what you use in Divinity: original sin during combat to Attack, use abilities or spells(you all knew im sure).
Max action points: is how many action points you can at maximum have at once,
the base is 7 action points, your max action points is increased by 1 for every CON you invest.
Formula for Max ability points: 7 + CON x 1 - 5
Formula with Lone Wolf: 9 + (CON x 1 - 5)
Starting action points: is how many points you start a battle with,
the base is 2 action points, your starting action points is increased by 0,5 for every PER and SPD you invest.
Formula for starting action points: 2 + (PER + SPD) x 0,5 - 5
Formula with Lone Wolf: Lone Wolf does not affect starting action points.
Recovery action points: is how many points you recover/gain every round,
the base is 3,5 action points, your recovery action points is increased by 0,5 for every SPD you invest.
Formula for recovery action points: 3,5 + SPD x 0,5 - 2,5
Formula with Lone Wolf: 5,5 + SPD x 0,5 - 2,5
TIP: if starting action points is 6,5 you will in an actuall fight recover 7 points not 6,5. this is also true for recovery action points.