Character roles within an adventuring team are important. If everybody decides to be a jack-of-all-trades, then the party generally won't be as successful as groups that split up roles to various members so that they can be mastered. This list gives examples of some of those roles.
Keep in mind that a character can take on multiple roles, and that by no means is the following list of roles exhaustive. Using many roles and coming up with one's own will be to the benefit of both the adventurer and her cohorts, as it means that a group can better react to changing circumstances.
A Direct Mêlée character focusses on dealing large amounts of damage with mêlée weapons. Even though this seems like a very narrow focus, there is a multitude of ways a character can go about doing this. For example, a duelist who specializes in Rapiers would qualify for this role just as much as a hulking warrior with a greatsword.
A Direct Ranged character is similarly focussed on causing damage, but through ranged weapons. The skill set is dramatically different; a good Ranged character must be able to cause a lot of damage and avoid any direct confrontation.
A Battlefield Shaper character's job is to disrupt and hamper opponents in order to set them up for attacks from other members of the party. This includes things like tripping opponents, moving opponents around using the Throw feat, disarming opponents, and using weaponry designed to discombobulate characters such as Nets, and Bolas. The primary goal of a Battlefield Shaper is to set opponents up for a devastating attack.
A Shadow tends to quietly duck away from combat once battle is joined, but they're not running away. A Shadow specializes in showing up where opponents least expect him and taking advantage of them when they are weak. These characters will focus on staying hidden, quickly acting, and then slipping back into the background.
Filling the Magical Assault role means that a character uses her magical power to directly harm and hinder opponents. From lightning blasts to fire storms, and even to mind-control, the number of ways to fill this roll are limited only by a player's imagination.
The Magical Control role is focussed around controlling the battlefield and changing it to be more advantageous to one's party. This can mean slicking down the floor with ice or literally reshaping the lay of the land to create walls and towers of earth and rock. This role is about creating areas of control and funneling enemies in.
The Magical Support character is the character who helps his companions with stat-boosting spells and healing magic. This is the character that quickly heals a maimed party member, throws up a protective barrier to deflect incoming arrows, and infuses the berserker's muscles with magical power.
This roll effectively serves as a party's eyes and ears when they would otherwise be in the dark. Magic Intelligence characters use remote viewing to scout ahead of their tracks, they talk to animals to learn what transpired when no human was looking, and they tap into opponents' minds and discover their intentions.
This is the character who is best at dealing with others. He tends to act as the group's representative when dealing with NPCs. The Face will negotiate with the innkeeper for cheaper lodging, distract the guard while the rest of the party sneaks past, and disguise himself to slip into the count's mannor undetected.
The Scout is most at home in the wilderness. Whether that be dense forests, soggy marshland, craggy mountains, or deep caverns, this character will guide her friends through the unknown safely. The Scout knows best how to travel her chosen terrain, knows the inherent dangers, and knows how to deal with the landscape's dangerous animals. She will often be further ahead, scouting out potential hazards and ensuring the safety of her friends.
The Mechanist is enamored by technology, and because of this is the perfect person to disable traps, pick locks, and disrupt machinery. On that same token, the character is also very resourceful, and is able to quickly construct quick contraptions to aid a party in it's travels.
This is the character that is looked to first when a group faces a new threat. The Loremaster knows not just the legends of the various peoples, but has also researched a great many supernatural phenomena and monsters. This character will help identify unfamiliar plants and monsters, recount tales of ancient relics, and let the party in on precisely how to kill the massive monster that has just burst from the forest.