Go to crutchfield.com, they have good explanations, but their prices are a bit steep. They will give you step by step instructions on disassembling and reassembling your car, but you can find those on these forums as well.Use them for research and then go find the same speakers cheaper somewhere else. I bought half my stuff from Walmart(used to work there, got discount) and sonicelectronix.com, but I've used eBay before too with good results. I just shopped around and saved about $70
My only advice for you is if you are replacing the front speakers: GET COMPONENT SPEAKERS AND NOT COAXIAL SPEAKERS. The difference is that component have a separate tweeter and a separate crossover which yield better audio results. Crutchfield.com will explain all these terms.
Goodluck! Have Fun, and Enjoy.