Bunions are growths of bone or tissue around the metatarsophalangeal joint of the hallux (big toe). As a result of this growth pushing on the joint in your big toe, it can bend or turn inwards toward the second toe, causing angulation ranging from a slight bend to the big toe bending entirely under the other toes.
As said, a bunion is either a bony anomaly or tissue related; the tissue is a swollen bursa sac. That sac is fluid filled and exists to minimize friction between bones and muscles.
As the swelling or growth progresses, the pain will obviously become worse, and perhaps more noticeably at first one will see the tilt in their big toe.