Book: Haynes - Automotive Electrical Manual - All Common Repairs...
http://www.themotorbookstore.com/el.html
(They may sell the above book at your local auto parts store???)
After you read the above, then buy a multimeter. You may decide to buy a multimeter with certain features once you learn a little about this.
But on the other hand, a multimeter with more features is going to have a big instruction book on how to use it. So might be easier to buy something simple to start out with.
I'll also give you a google search link for how to use a multimeter. But if you click on a page which has a lot of math formulas and looks like only Einstein would understand it, forget about that page and find another which explains things in easy to understand basic instructions.
Multimeters can be used for simple automotive wiring testing, the instructions for how to do this can be simple and basic, and most people can learn to do this with a bit of reading. However multimeters are also used for complex electronic circuits and you guys don't need to bother with learning any of that stuff.
How to use a multimeter...
http://www.google.com/search?hl=en&s...imeter&aqi=g10