To suck is to draw something by force. Vacuum cleaners suck dirt from the floor and milkshake drinkers suck this liquid, tasty liquid through a straw.
Drinking something by pulling it into your mouth is to suck it. You can also suck on something, like a peppermint or a thumb, by holding it in your mouth. Objects can suck too — a fan sucks warm air out the window. You can also suck someone into your plans, meaning you force them to participate. The word suck comes from the Proto-Indo-European sug, from the sound your mouth makes when you suck on something.