Anyone who has ever tried to remove an oil spot from a driveway or garage floor knows that it's a good idea to figure out where an auto leak is coming from and what it is before it gets out of control. In addition to creating unsightly messes, leaking fluids can be a sign of a car in need of repair. Many automotive experts recommend using a large piece of cardboard (preferably white, but any type will do in a pinch) to identify the source of the leak.
Simply slide the cardboard under the car and check it the next morning for the color and texture of the spots. Engine oil will be oily and black, whereas brake fluid is oily and clear. Coolant leaks are usually green or yellow, and transmission fluid is typically red in color [source: Warranty Info]. It makes your mechanic's job considerably easier if you provide these types of details instead of just complaining vaguely of "some type of leak, coming from somewhere in the car."