Handicap: everyone is racing each other, times are corrected for the type of boat you are using, so where you finish on the water isn't necessarily your final position. Held on summer Saturdays (two races), Sundays (three races) and summer Wednesdays. Plus the sprint series on the 3rd sunday of the month in summer. (See also personal handicap below)
Class: you are only racing the people in your class, everyone else is just an obstacle to progress (although you must apply the rules!) Where you finish on the water relative to the others in your class is what matters. Open races and selected Sunday mornings.
Pursuit: starts are timed according to boat types, with the slowest boat leaving first. If everybody was equally good and got constant wind, all the boats would cross the line simultaneously. Again, where you finish on the water is your final position. Held once a month on the first sunday of the month, often a charity race so drop your pound in the box before starting.