Depending on which area of the car you're interested in, there are a few options - in terms of how a car works generally, it's hard to find a single book that covers it all in a very general sense, because as soon as you ask a few questions you have to go into some depth, and if you did this for a whole car you have a big book!
For a very brief overview of certain areas (i'm guessing you have a general idea of the concepts involved with what makes a car work - engine, gearbox, wheels, steering etc. but are looking for specifics about each areas' design and function?) the internet is your best friend - wikipedia, howstuffworks and google all work well and often can give an overview.
For books specifically -
Vehicle dynamics (steering, suspension, ride etc) - "Fundamentals of Vehicle Dynamics" by Gillespie is a good book. Refers more to road cars than race cars, but the mechanics is the same.
I'm sure other people can recommend books for powertrain, gearboxes etc. basically the more specific you get the more detailed your book will be