To lick is to taste or touch with the tongue. When your dog licks you, he's saying hello. Humans should opt for waving hello over licking.
Animal mothers lick their babies to clean them, and adult cats also groom themselves this way. People generally lick things to taste them: you might lick an ice cream cone or a lollipop, or lick salt off your arm after a day at the beach. Colloquially, to lick an opponent is to beat them at a game or fight. In jazz music, a lick is a short burst of music, or a solo.