At the Yawning Portal Inn (OOC)
Sailor, Brankx explanation is right, but he forgot the first part, you need a character first. Perception is one of the skills a character can take, that is based on Wisdom. Once your character is built, you will have a basic bonus consisting of your Wisdom modifier+proficiency bonus (if you are trained), to add to your D20 throw.
If you need help to create your character, please ask!