A creature with resistance to a damage type has the ability (usually extraordinary) to ignore some damage of a certain type each round, but it does not have total immunity. This almost always applies only to types of energy damage.
Each resistance ability is defined by what damage type it resists and how many points of damage are resisted. It doesn’t matter whether the damage has a mundane or magical source.
When resistance completely negates the damage from an attack, the attack does not disrupt a spell. Resistance from multiple sources usually does not stack.