Intro to 4th ed rules: Classes

Ok so I figured I'd post some basic rules and major changes to 4th ed from 3.5, I plan on doing this in a few posts. This one will be about classes.

Each Class has a role, this is kinda of where they fit in the party, and what they're good at. Controllers, Defenders, Leaders, and Strikers
Controllers deal with large numbers of enemies at the same time. They favor offense over defense, using powers that deal damage to multiple foes at once, as well as subtler powers that weaken, confuse, or delay their foes
Defenders have the highest defenses in the game and good close-up offense. They are the party’s front-line combatants; wherever they’re standing, that’s where the action is. Defenders have abilities and powers that make it difficult for enemies to move past them or to ignore them in battle.
Strikers specialize in dealing high amounts of damage to a single target at a time. They have the most concentrated offense of any character in the game. Strikers rely on superior mobility, trickery, or magic to move around tough foes and single out the enemy they want to attack.
Leaders inspire, heal, and aid the other characters in an adventuring group. Leaders have good defenses, but their strength lies in powers that protect their companions and target specific foes for the party to concentrate on.
Clerics and warlords (and other leaders) encourage and motivate their adventuring companions, but just because they fill the leader role doesn’t mean they’re necessarily a group’s spokesperson or commander. The party leader—if the group has one—might as easily be a charismatic warlock or an authoritative paladin. Leaders (the role) fulfill their function through their mechanics; party leaders are born through roleplaying.

With the introduction of Player's Handbook II that brings the number of character classes up to 16. They break down into their roles like this:
Controllers: Wizards, Druid, Invoker
Defender: Paladin, Fighter, Warden
Striker: Ranger, Rouge, Warlock, Avenger, Barbarian, Sorcerer
Leader: Cleric, Warlord, Bard, Shaman

Some of the Player's Handbook II classes, can be tailored to fit a secondary role if it picks certain feats, and powers.

Power Source:
Every class relies on a particular source of energy for the “fuel” that enables members of that class to use powers. The four power sources associated with the classes are arcane, divine, primal and martial.
Arcane: Drawing on magical energy that permeates the cosmos, the arcane power source can be used for a wide variety of effects, from fireballs to flight to invisibility. Warlocks, Bards, Sorcorers and wizards, for example, use arcane magic. Each class is the representative of a different tradition of arcane study, and other traditions exist. Arcane powers are called spells.
Divine: Divine magic comes from the gods. The gods grant power to their devotees, which clerics, avengers, invokers and paladins, for example, access through prayers and litanies. Divine magic excels at healing, protection, and smiting the enemies of the gods. Divine powers are called prayers.
Martial: Martial powers are not magic in the traditional sense, although some martial powers stand well beyond the capabilities of ordinary mortals. Martial characters use their own strength and willpower to vanquish their enemies. Training and dedication replace arcane formulas and prayers to grant fighters, rangers, rogues, and warlords, among others, their power. Martial powers are called exploits.
Primal: Primal powers draw on the innumerous spirits of the wild. Some primal powers are more overtly magical than others, but they all draw on the spirits of nature that pervade the worlds and, to come extent, the exho plane known as the Feywind. Primal powers are called evocations, because primal characters evoke primal spirts to make attacks and effect the world. Some characters channel primal spirits through their bodies in order to transform themselves and make their physical attacks more powerful. Other characters evoke primal spirts to create external effects.

These are just a few things to think over if you wanna roll up a new 4th edition character.