At first level, your character gains a number of skill ranks dependent upon your class plus your Intelligence modifier. At every level after that, you gain additional skill ranks. These skill ranks can be spent on any skill, but you can only invest a number of ranks into a specific skill equal to your total Hit Dice. In addition, each class has a number of favored skills, called class skills. Your character is most proficient in these skills, as they represent part of his professional training and constant practice. You gain a +3 bonus on all class skills that you put ranks into. If you have more than one class and both grant you a class skill
bonus, these bonuses do not stack.