What are the main differences between a pigeon a seagull and a duck?

A pigeon, feral, wood or "stock dove" fly with a push and glide motion. Seen on land, rarely around water.

A seagull, does not exist as a species. A gull is the correct term, a "glider" in bird terms. Generally above water, usually the sea, but now associated with land fill sites.

A duck is a water based bird which spends a lot of time on the water.