Stats

Strength: Your physical power. The higher your strength, the more you can carry, and the more you can dish out during combat. It also factors into your HP.
Increase by: Using the exercie machine, fighting.

Intelligence: The mind can be a powerful thing. Intelligence increases the effectiveness of your magic. It also factors into your MP.
Increase by: Using magic, learning things, solving puzzles.

Agility: Cat-like reflexes can save your hide in a dangerous situation. Agility regulates your speed, as well as your abilities to do physical manuevers. It also factors into your SP.
Increase by: Fighting, using thief skills.

Vitality: Still the most important stat in the game. Vitality is your physical endurance; the higher it is, the less damage you take. It also factors into your HP and SP.
Increase by: Doing any physical action, fighting.

Luck: I have no idea what this does. The game doesn't spell it out, and it hasn't really affected my games at all, so I can't tell you about this. If anyone knows what it does, e-mail me.
Increase by: Doing anything.

Communication: Remember that one game where this was useful? Well, it isn't this one. This has NO USE WHATSOEVER! Take my word on this one.
Increase by: Talking.

Weapon Use: Any idiot can stick a sword into something, but only a true master knows where to stick it for the most damage. Weapon Use is how skilled you are with your weapon.
Increase by: Attacking in combat.

Parry: This skill allows you to block attacks with either your shield or a weapon. Since only Fighters and Paladins get a shield, they're the only ones that really have a use for this.
Increase by: Blocking in combat.

Dodge: In this game, dodging comes in two forms: either ducking (avoid high attacks) or jumping (avoid low attacks). This is how skilled you are with these tactical manuevers.
Increase by: Dodging in combat.

Stealth: The first thief skill, and the most important one. This allows you to "sneak" around, thus making less noise. Outside of stealing, this can also reduce the amount of random encounters you have.
Increase by: Sneaking around.

Lockpicking: Some rude people like to put locks in the way of your treasure. This thief skill allows you to get past these annoyances. This also factors into how well you can disarm traps.
Increase by: Picking locks.

Throwing: Your skill with ranged weapons. Fighters and Thieves can both use this to full effect, whether they're using rocks or daggers.
Increase by: Throwing stuff.

Climbing: With this ability, walls will no longer be able to block you. Thieves start with it, but Fighters and Paladins can read a book that teaches the skill.
Increase by: Climbing stuff.

Acrobatics: A new skill aimed solely at Thieves. This allows you to jump. This may not sound spectacular right now, but if you build it up enough, you should be able to leap tall buildings in a single bound.
Increase by: Jumping.

Magic: This is required to use any Magic. It regulates how useful your spells are. It also factors into your MP.
Increase by: Casting spells.

Honor: The measure of just how heroic you really are. Honor goes up with your good deeds, and down with your bad ones. Also, you cannot spend points on this; you have to earn it.
Increase by: Doing good deeds.

Health: Your HP. You lose some of this when you get damaged or do an action with no SP. When it reaches zero, you're dead. You can recover it by using Healing Potions and resting.
Increase by: Raising Strength and Vitality.

Stamina: Your SP. It goes down with every physical action you do. When it reaches zero, you begin to lose HP in its place. You can recover this by either resting or getting into combat (don't ask why).
Increase by: Raising Agility and Vitality.

Mana: Your MP. You lose some whenever you cast a spell. When it reaches zero, you can no longer use magic until you recover it. You can get it back by eating a Mana Fruit or sleeping.
Increase by: Raising Intelligence and Magic.