CREATING A NEW CHARACTER
Creating a new character in Planescape: Torment is quite simple. You begin with 9 points in all stats plus 21 points to distribute freely. You can raise each stat to 18 but no higher, except for Strength which can be raised to 18/100, and you can't lower your stats below 9. If you think 21 points is a bit low, don't worry. You will gain one stat point to distribute freely each time you level up.
I can almost hear you asking, "Don't I get to choose a name, a class, an alignment, general appearance, etc.?" No, you don't. Your character is called Nameless One, he starts the game as a 3rd level Fighter, and his initial alignment is True Neutral. And sorry – you can't change his looks either. You can change your class later in the game by speaking to certain people, and your alignment most probably will change based on your actions during the game. Please see the Gameplay and Tips page for more information.
Distribution of Stat Points
So, how should you distribute your stat points? That depends entirely on what kind of character you want to play. Do you intend to play a clever mage? A dumb brute? An idiot? A cunning thief?
Strength is a measure of your physical strength: How much you can lift and carry, and how hard you can punch a target. This is the most important stat for a fighter and is also useful for intimidating those who cannot be persuaded through gentler means.
Intelligence tells how smart you are. A high Intelligence gives you more dialog options, helps you solve riddles and quests, and if you are a mage it allows you to scribe more spells in your spell book. If you are planning to play as a mage, you should go for a high Intelligence.
Wisdom helps you learn from your experiences. A high Wisdom grants you a bonus on all experience points you earn so you gain levels faster, and it allows you to choose better dialog options by warning you if you are about to say something that might not go down well with the person (or creature) you're speaking to.
In Planescape: Torment, a high Wisdom also helps you regain memories from your earlier lives, which makes Wisdom the most important stat in this game.
Constitution is a measure of your general health. With a high Constitution you will have more hit points, and you will heal faster in the likely case that you are injured. It is a useful stat for all classes in combat but you can live with a low Constitution since fighting is not central in Planescape: Torment.
Dexterity tells how nimble you are. A high Dexterity gives you a better (that is, lower!) Armor Class, which is important to fighters, and it grants mages a better chance to get their spells off. But it benefits the thief most of all by giving him a better chance to hide in the shadows or pick somebody's pocket without getting caught.
Charisma tells how charming you are. A high Charisma allows you to bluff or convince people to help you, it makes them believe even the most outrageous lies, and it earns you a better reward for services rendered. For example, the size of the reward you earn for tracking down a thief in the early part of the game depends on your Charisma.
[Thanks to kmonster for excellent comments and corrections to the stat descriptions!]
Once you have finished creating your character, it is time to start the game in the ... the Mortuary?