Mutual grooming is one way that cats show affection for each other. When you pet them, they interpret that as grooming, and so when they lick you, they're really just petting you back.
Also, when they rub against you, part of what they're doing is marking you as their territory by leaving their scent on you. It's only fair, you know; we use collars and tags and microchips on them. Every single day, as soon as I get out of the shower, Squijum is right there rubbing all over me. Having just washed all his scent off myself, you see, I must immediately be re-marked.
Usually Squijum strews my tatted pieces across the living room during the night. Last night he decided to stack them neatly instead.