Buy a cheap car (i.e. a MX5/Miata) and go racing (on a racetrack). Stuff will break and you will have to fix it, since it's not your daily car there is no pressure in having it fixed on time, just take your time and figure out how to fix whats broken. Youtube is a great source for instruction videos. Even if the car does not break, you will still need to wrench on it to upgrade the brakes, engine, transmission, suspension etc, make it more suitable for racing. In the end you'll have the knowledge, a racecar, a great new hobby, a lot of fun and meet a lot of cool people.

I would start with a cheap OBDII reader ($50 or less) that has a real-time feature that can show you what all the sensors (o2, intake temperature, etc) are saying.

That's a more fun start than a book, and it might lead you in a certain direction as to which book you might want to read.

You could always play "Car Mechanic Simulator 2015". Not 100% accurate but it does teach a lot if you come in with no knowledge whatsoever.