Classes are what determine one's initial attribute allocations, starting Soul Level, and initial equipment in Demon's Souls.
"Soul Level" is your "Experience Level". The higher your Soul Level, the more each stat point costs from the Maiden in Black. "Starting Soul Level" affects how expensive stat upgrades are right off the bat. At level 1, the Royalty has the lowest initial cost for stat upgrades, while the Thief and Barbarian have the highest, at 9.
The Knight lacks in physical stats compared to other fighting classes, but makes up for it somewhat in his comparative mental refinement. He can access both miracles and magic without much work and starts with a versatile equipment set. His decent starting armor makes sure you're protected until you are able to find more. It is a good choice for beginners.
Thieves happen to start off with more luck than any other class. They have good dexterity which opens up for better opportunities at higher levels. They should stick with light armor, which enables them to roll, since they're not really big on blocking. Because of the ability to move faster, thieves can get easy back stabs which usually kills the enemy. On the other hand if thieves are attacked they suffer an intolerable amount of damage. Evading is the best option as a Thief.
Main magic class, but lacks the passive MP regeneration item of the Noble class. Starts with the spells Water Veil to reduce fire damage and Flame Toss for offensive means. Is among the tougher classes to start with.
This is perhaps the best choice for starters. Temple Knights have a moderately high attack, and utilize the power to call on God to heal or protect him in battle. These are known as miracle powers. Temple Knights have great starting armor, and one of the best small starting shields in the game, with a 100% block chance.
The basic balanced class, it has balanced stats with highs in physical stats at expense of intellect. Those who want an easier time at the game might consider this class.
A hybrid of the Thief class. Very high Agility provides a better offense, but you don't have ready access to magic.
Very high starting strength and hit points, but poor equipment. Ideal if you plan on playing a brute force character, possibly emphasizing large two handed weapons. Not recommended for beginners.
Ideal character for beginners. The coronet increases MP and the ring regenerates it. Royalty starts with the Soul Arrow spell which deals high damage to armored foes. This is the only character that starts at Soul Level 1.
Small boosts to Luck and most stats make this a fairly balanced class overall. You can melee or use the bow with proficiency (bows can also be aimed first person, and have some zoom ability), consider this as an alternative class to the Soldier if you enjoy ranged classes.