There is a lot of fluff (flavour) in the core rules, so this a condensed summary

Characters in Pathfinder belong to a class (job). There are many classes and some overlap and differ slightly.

In D&D there are 6 ability scores, which are used differently depending on what class one is some are useless, other are essential.Physical: Strength, Dexterity, ConstitutionMental: Wisdom, Intelligence, Charisma

Pathfinder does not have team roles as guidelines (unlike D&D4), but it is helpful to get the basic idea of what makes a good party where nobody treads on each others toes. In 4e there they are divided into controller (which affect enemy), defender (aka. tank), leader (eg. healbot, buff/debuffer) or striker.

A spellcaster casts magical spells and are based off one of the three mental abilities (Int, Wis, Cha). They can be spontaneous (you pick known when you level) or prepared casters (you pick in the morning).Spells can be divine or archane the former is granted by a god and can be cast in armour, while the latter has a spell failure % in armour wizards (arcane) wear cloth, while paladins (divine) are clad head to toe in heavy armour.Many spells of various classes overlap, but there is a lot of diversity.A psionic cast psychic spells (correctly called powers) in much the same way, but are a bit of an addition that doesnt really fit in.

Every level you get more hit point, which are determined based on hit dice (HD). Different classes get different hit dice (NB. Pathfinder has dice increase by 2 compared to D&D 3.5; also monsters have racial HD which is doesnt depend on class):d6 sorcerers and wizardsd8 monks, bards, clerics, rogues and druidsd10 fighters, paladins, rangersd12 barbarians

These also affect how good your attack bonus is (Base attack bonus, BAB).Additionally there are three saves fortitude (based off constitution), reflex (based off dexterity) and will (based off wisdom). Classes have good save and bad saves. For example, a wizard has a good will save, but poor fortitude and reflex, while a fighter has a good fortitude save, but bad will and reflex save. So a wizard would be bad at ducking a fireball (refl) or resisting a poison (fort), but good at resisting enemy spells (will), while a fighter would be good at resisting poisons, but not spells.

Weapon and armour proficiency depends on the class too. Fighters can use basically any weapon, while wizards cannot.

Different classes require different amount of prep. Monks are very simple, while spellcasters need some study of spells needed. Fighters are highly customisable too. Also unlike 4e or WoW the classes are not balanced: wizards are way better than alchemists.Online there are many guides on how to use each class (simply google pathfinder guide bard for example).

Below are classes with fluff in italics (copy-pasted) and some semi cryptic notes and a list of importance of the various abilities for that class.

D1210 HDBarbarian: The barbarian is a brutal berserker from beyond the edge of civilized lands.Rage based Tank (they buff when they rage, but get fatigued from it).Str>Con>Dex>Wis>Int>Cha.

Fighter: Brave and stalwart, the fighter is a master of all manner of arms and armor.Technical prowess based Tank (gain an extra feat every level). Str>Con>Dex>Wis>Int>Cha

Paladin: The paladin is the knight in shining armor, a devoted follower of law and good.Tank with limited Cha-spellcaster (divine) and healing. Special mount (= riding animal, eg. horse).Str>Cha>Con>Dex>Wis>Int

Monk: A student of martial arts, the monk trains his body to be his greatest weapon and defense.Unarmed Tank (martial arts). special move: flurry of blows (many karate attacks)Str>Wis>Dex>Con>Int>Cha

Cavalier: Mounted upon his mighty steed, the cavalier is a brave warrior, using his wit, charm, and strength at arms to rally his companions and achieve his goals.Mounted Tank.Dex > Str > Con > Cha > Wis > Int

Samurai: ???Tank (gives some buff). Str>Dex>Con>Wis>Int>Cha

Soulknife: A warrior who creates a unique weapon out of mental energy.Psionic tank with a mental weapon (kind of cool if given a chance)

Psychic Warrior: A soldier who combines psionic power with physical prowess.Wis based psionic

Ranger: A tracker and hunter, the ranger is a creature of the wild and of tracking down his favored foes.Good at killing particular creatures and with limited Wis spellcaster (Divine).Dex>Str>Wis>Con>Int>Cha

D8 HDCleric: A devout follower of a deity, the cleric can heal wounds, raise the dead, and call down the wrath of the gods.Healbot tank. Wis Spellcasting/Cha channelling (divine). Special move: channel (cures folk in a cone). Wis>Cha>Con>Int>Str>Dex

Magus: There are those who spend their lives poring over ancient tomes and texts, unlocking the power of magic, and there are those who spend their time perfecting the use of individual weapons, becoming masters without equal. The magus is at once a student of both philosophies, blending magical ability and martial prowess into something entirely unique, a discipline in which both spell and steel are used to devastating effect. As he grows in power, the magus unlocks powerful forms of arcana that allow him to merge his talents further, and at the pinnacle of his art, the magus becomes a blur of steel and magic, a force that few foes would dare to stand against.Melee with Int Spellcasting. Special moves: spell combat (spellcast and attack at the same time) and spellstrike (imbue a weapon with a touch attack spell: when it hits the weapon deals damage and the spell goes off).Dex>Int>Con>Wis>Str>Cha

Summoner: Bonded to a mysterious creature called an eidolon, the summoner focuses his power on strengthening that connection and enhancing his strange, otherworldy companion.The Eidolon (summoned creature) acts as a tank, while the summoner is a Cha Spellcasting.Cha > Con > Dex > Wis > Int > Str

Alchemist: The alchemist is the master of alchemy, using extracts to grant him great power, mutagens to enhance his form, and bombs to destroy his enemies.Crafter/Artillery. Int > Dex > Str > Wis = Cha > Con

Gunslinger: For a renegade few, battle sounds different than it does for the typical fighter. The clash of steel and the sizzle of spell energy are drowned out by the thunderous rhythm of gunfirethe pounding beat of the gunslinger.Artillery. Dex>Wis>Con>Int>Str>Cha (Mysterious stranger: Dex>Cha)

Rogue: The rogue is a thief and a scout, an opportunist capable of delivering brutal strikes against unwary foes.Skill monkey. Special move: sneak attack (deals extra damage when unnoticed). Dex>Con>Str>Wis>Int>Cha

Ninja: ???Skill monkey. Cha>Dex>Con>Str>Wis>Int

Bard: The bard uses skill and spell alike to bolster his allies, confound his enemies, and build upon his fame.Buffer thanks to bardic performances and Cha Spellcasting (archane).Cha>Dex>Int>Con>Wis>Str

Druid: The druid is a worshiper of all things naturala spellcaster, a friend to animals, and a skilled shapechanger.Shapechanger and Wis Spellcasting (divine).Wis > con > dex = str > int > cha

Inquisitor: Scourge of the unfaithful and hunter of horrors, the inquisitor roots out the enemies of her faith with grim conviction and an array of divine blessings.Buffer and Wis Spellcasting.Wis > Dex > Str > Int > Con > Cha

D6 HDWizard: The wizard masters magic through constant study that gives him incredible magical power.Artillery. Int Spellcasting (Archane). Int>Dex>Con>Wis>Str>Cha

Sorcerer: The spellcasting sorcerer is born with an innate knack for magic and has strange, eldritch powers.Artillery. Cha Spellcasting (Arcane). Cha>Dex>Con>Wis>Int>Str

Oracle: Drawing upon divine mysteries, the oracle channels divine power through her body and soul, but at a terrible price.Artillery. Cha Spellcasting. Hindered by a curse (chosen from a list). Cha > Con > Dex > Str > Wis > Int

Witch: Lurking on the fringe of civilization, the witch makes a powerful connection with a patron that grants her strange and mysterious powers through a special familiar.Artillery. Int Spellcasting. Int > Con > Dex > Wis > Cha > Str

Psion: A master of the mind, a seeker of knowledge of psionics.Int based psionic

Wilder: A natural talent with psionics who channels emotion to wield uncontrolled power.Cha based psionic