Have a look through my Links page to see various types of events ... I have my Links pages arranged by categories.
http://www.machka.net/links.htm
But in brief, very generally, and with
approximate distances listed for the races ...
Time Trial - a short race (10-40 km) where they set riders off one at a time and the riders race against the clock
Crit - a short loop race where riders race round and round a short track (2-3 km) and try to lap each other
Road Race - a longer race (50-100 km) where a group of riders sets off and tries to reach the finish line first
24-hour Time Trial - a long race where riders set off in a group but have to separate themselves so no one is riding within drafting range of another rider soon after the start. The idea is to ride as much as possible in a 24 hour period.
Randonnee - one of many long distance rides ...
rides, not races ... where cyclists have to maintain a certain minimum speed in order to successfully finish. There are 50 km, 100 km, and 150 km populaires, and 200 km, 300 km, 400 km, 600 km, 1000 km, and 1200 km randonnees (brevets).
Century - a casual 100 mile ride done solo, with a friend, or with a group of people. There are some organised centuries which attract a lot of riders, many areas have an annual century ride.