Every class is fully capable on its own, and you can customize your character however you want, but classes fall into roles they generally excel in.
The source also lists these building blocks for roles: weaponry, protection, support, divine, arcane, primal, psionic, movement, social, tactics, utility.
Vanguard
The warrior classes, masters of melee combat. They generally have the best protection and excellent close-up offense, and are the primary front-line combatants. They have abilities that help allies maneuver around the battlefield and make things difficult for enemies. Vanguard classes get attacks of opportunity.
Berserker · Soldier · Martial Artist · Guardian
Paragon
The mage classes, the most proficient in their magical origin. Potent spellcasting: they can affect large areas and deal with groups of enemies at once through crowd control, hazardous terrain, or hampering foes. Full spell list.
Arcanist · Cleric · Druid · Psion
Specialist
Experts in certain tasks or skills, usually favoring cunning over brawn. Versatile, skill-based classes, normally with high utility and single-target damage. Bonus skill points.
Artisan · Sage · Ranger · Rogue
Gifted
Versatile support classes: status effects and social situations. They inspire and assist other characters. They have good offense and defense, but their strength is in powers that protect allies and reveal enemies’ vulnerabilities.
Bard · Duskblade · Sorcerer · Warlock
Role names
One version of this section calls the roles “the warrior, the mage, the expert, and the gifted”; the other calls them Vanguard, Paragon, Specialist and Gifted. This page uses the second set.
Each class needs
Every class entry in the source ends with “In exploration []. In social situations []”: each class still needs its exploration and social hooks (see Design Pillars).