In AQ3D, stats are divided into three groups. The first group, being the most important one, are the main stats. These are the Health, Mana, Attack, and Defense statistics. The second group is called the Bonus stats, which are Dodge, Hit, Crit, and Crit Power. The last group is the Resists stats, which are currently unused.
If you are looking for all the items in-game with stats, you can find them on the Item Stats Chart.
Health, also known as the "red bar" on your character box, is the determining factor of the amount of damage you can take. It gets reduced when you are attacked and hit by enemies. Once you reach 0 Health, you will die and you must wait 10 seconds before you are able to respawn. Health is naturally regenerated outside of combat, and can also be regenerated with the use of certain class skills and potions.
Mana is also known as "that blue bar beneath your health". Mana allows you to cast class skills that consume Mana. Mana will naturally regenerate overtime, but will regenerate slower while in combat. Mana can be also be regenerated by using potions.
All the mana usage costs for each class can be found here.
Attack determines how much damage you can do to an opponent. The much stronger your attack, the more damage you can inflict.
Defense determines the reduced amount of incoming damage you take during combat. The stronger your defense, the weaker your opponents attacks are.
Dodge determines your evasion chance, which allows you to avoid incoming attacks that would normally inflict damage to you.
Your Hit percentage determines how likely you are able to inflict damage to a target, before any other modifiers.
The crit percentage determines the likeliness of dealing additional bonus damage on any attack you inflict on your opponent.
Crit Power will determine how strong the additional bonus damage you receive on a critical hit will be.