Archer is a sub-class concerning mainly warrior but nothing prevents mage to become one in condition of having a minimum of 50 dexterity. Being archer allows mainly to attack from far in order to prevent others of moving or casting a spell.
Damage is calculated in function of :Battle Mage is a sub-class mixing warrior and mage so a warrior with mage's spells or a mage using weapons.
He can invest points either :
Paladin is a sub-class mixing warrior and priest so a warrior with priest's spells.
He is able to use all weapons but can't acquire all spells requiring more than 80 charisma.