Like many competitive sports, there are various levels of gliding competitions, ranging from regionals (the lowest) to the Worlds (the pinnacle). In the UK, the competition season starts in May and runs through until early September. Abroad, it just depends on how good the weather is! South Africa, Arizona and Australia are all hot and give many good days. World competitions are generally held in countries that have guaranteed good weather (not England!).
Most competitions are limited to a maximum of 50 gliders (for safety reasons). Each day (one task) has a maximum score of 1000 points for the winner; this can be devalued if very few gliders get around the task (the idea being that if only a small proportion of gliders get home, then luck probably had a lot to do with it!). The scores are assigned according to the speed relative to the winner.
As the name suggests, this is held locally and is generally the first serious competition that budding racing pilots enter. It is normally held over 9 days and is handicapped, i.e., each glider has an assigned handicap rating according to its calculated performance (an old wooden glider may have a handicap of about 80, whereas a modern machine may have one of about 109). To enter the competition, a pilot must have a minimum qualification called a Silver C (to have reached this level, the pilot must have passed written exams, completed a 50 k solo flight, stayed aloft for 5 hours in one go and made a height gain of 1000 meters). The competition is usually run and organised by one of the bigger clubs in the region. Pilots pay an entry fee and can win day prizes. The pilots' final position in the competition dictates their nationals rating (see below). .
To enter a nationals, a pilot must have first gained a nationals rating. This is obtained by doing well in a regional contest (usually means finishing in the top 3 or 4). In the UK, there are 5 (6, if you include the juniors) nationals competitions which are split according to glider performance. Starting with the lowest performance they are: the club class (gliders with a handicap of 104 or under, so wingspan is not important); the standards (gliders must not have a wing span of greater than 15 m and must not have operable performance-enhancing flaps); 15 m (as standards, but flaps are allowed); 18 m (wingspan limited to 18 m, but flaps are allowed); open class (anything goes - wingspans of 27 m are not unheard of). All national competitions are un-handicapped, apart from the club class. The aim of the club class is to encourage high level competition using older and therefore cheaper gliders of differing performances. Club class gliders are also prohibited from carrying extra water (as modern gliders can often carry more and therefore have an unfair advantage).