Spell slots in the Pathfinder tabletop game work a bit differently than in other RPGs. A spell slot is not an ability score, and it does not have a cooldown like a magic item. Instead, each spell requires a certain number of spell slots, and each spell can be used only once per day. To use a spell, you must first cast it from your spell list, which you can do by expending one or more of your spell slots. The number of slots you expend is based on the level of the spell you are casting.
For example, casting a 1st-level spell requires one slot, while casting a 3rd-level spell requires three slots. Once you have cast the spell, it is gone for the day and cannot be used again until you spend another slot to cast it again. Unlike other RPGs, spells in Pathfinder do not have an unlimited number of uses. If you attempt to cast a high-level spell using too few slots, the game throws an error message and your character cannot cast that particular spell.
