Basic:

 Ranged attack damage is increased by 10%

Advanced:

 Ranged attack damage is increased by 25%

Expert:

 Ranged attack damage is increased by 50%

Basic:

 In a siege, the catapult's shots, damage, and accuracy are increased:  1 shot + extra damage

Advanced:

 In a siege, the catapult's shots, damage, and accuracy are increased:  2 shots + extra damage

Expert:

 In a siege, the catapult's shots, damage, and accuracy are increased:  2 shots + max damage

Basic:

 Allows the hero to bribe army camps.  The higher the skill, the more that join:  25% join

Advanced:

 Allows the hero to bribe army camps.  The higher the skill, the more that join:  50% join

Expert:

 Allows the hero to bribe army camps.  The higher the skill, the more that join:  100% join

Basic:

 Gives the hero a chance to learn a spell cast by an enemy spellcaster:  20%  (2nd level max)

Advanced:

 Gives the hero a chance to learn a spell cast by an enemy spellcaster:  30%  (3rd level max)

Expert:

 Gives the hero a chance to learn a spell cast by an enemy spellcaster:  40%  (4th level max)

Basic:

 The hero begins to generate money as if he were a small town:  100 gold per day

Advanced:

 The hero begins to generate money as if he were a small town:  250 gold per day

Expert:

 The hero begins to generate money as if he were a small town:  500 gold per day

Basic:

 Grant's the hero a bonus to morale.  (necromancers cannot learn this skill) :  +1 morale

Advanced:

 Grant's the hero a bonus to morale.  (necromancers cannot learn this skill) :  +2 morale

Expert:

 Grant's the hero a bonus to morale.  (necromancers cannot learn this skill) :  +3 morale

Basic:

 Gives the hero extra land movement:  +10% movement

Advanced:

 Gives the hero extra land movement:  +20% movement

Expert:

 Gives the hero extra land movement:  +30% movement

Basic:

 Grant's the hero's army a bonus to luck in combat:  +1 luck

Advanced:

 Grant's the hero's army a bonus to luck in combat:  +2 luck

Expert:

 Grant's the hero's army a bonus to luck in combat:  +3 luck

Basic:

 Increases the rate per turn that a hero regains spell points:  2 spell points per turn

Advanced:

 Increases the rate per turn that a hero regains spell points:  3 spell points per turn

Expert:

 Increases the rate per turn that a hero regains spell points:  4 spell points per turn

Basic:

 Increases the hero's movement on water:  +50% movement

Advanced:

 Increases the hero's movement on water:  +100% movement

Expert:

 Increases the hero's movement on water:  +150% movement

Basic:

 Animates a portion of the units killed in battle into skeletons when you win:  10% of killed units

Advanced:

 Animates a portion of the units killed in battle into skeletons when you win:  20% of killed units

Expert:

 Animates a portion of the units killed in battle into skeletons when you win:  30% of killed units

Basic:

 Reduces the movement penalty of the hero over rough terrain:  Reduces penalty by 25%

Advanced:

 Reduces the movement penalty of the hero over rough terrain:  Reduces penalty by 50%

Expert:

 Reduces the movement penalty of the hero over rough terrain:  Reduces penalty by 100%

Basic:

 Increases the visibility radius of the hero in the Adventure Window:  +1 square

Advanced:

 Increases the visibility radius of the hero in the Adventure Window:  +2 squares

Expert:

 Increases the visibility radius of the hero in the Adventure Window:  +3 squares

Basic:

 Allows the hero to learn higher than 2nd level spells:  3rd level spells maximum

Advanced:

 Allows the hero to learn higher than 2nd level spells:  4th level spells maximum

Expert:

 Allows the hero to learn higher than 2nd level spells:  5th level spells maximum