Competitions involve a group of gliders flying the same task. The winner is the fastest one around the task. Scoring is simply taking the distance of the task and dividing it by the time taken.
Often the difference between first and second place is seconds. Over the course of the week these differences get added up, and the fastest pilot overall wins.
Modern high performance gliders cruise between thermals at speeds in excess of 90 mph. When the thermals are strong, a good pilot can average more than 80 mph over a task of a several hundred miles! Fancy a quick trip to Wales?