Perception reflects what a character can See, Smell, Taste, Touch and Hear, as well as their ability to hit targets at a distance.
Add your Character's PER Mod to their Initiative rolls.
When your Character needs to notice something about their surroundings in general, they will often make a Perception Check by rolling 1d20 plus their PER Mod.
When a Character wants to explore deeper into something they are perceiving, they or the GM can opt for them to roll an appropriate Sense Skill Check.
When at 0 , a character lose all sense of touch, taste, sight, hearing and smell.