Touring car racing is a competitions in heavily-modified street cars. Cars are usually 4-door 'family' sedans or, more rarely, 2-door coupe cars.
Cars are separated into groups of similar performance level. There are short "sprint" races and many touring car series include one or more "endurance" races. These endurance races last anything from 3 to 24 hours and are a test of reliability and pit crews as much as car and driver speed.
Rules vary from country to country. For most series it is required that the competitors start with a standard body shell but it seems like just about anything goes from there on out. Virually every other component is allowed to be heavily modified for racing, including engines, suspension, brakes, wheels and tires.
For race enthusiasts who enjoy handling and speed, it's all about driving your car as fast as you can around curves, uphill and down, while enjoying the acceleration, braking, and cornering of your car. Before you try to get into a race, you might want to go to a driver's school to pick up some pointers.