If you're not handy with tools and DIY stuff for cars, the only way it's going to come out okay is to buy a system and let the place you bought it from install it. I have no idea what kind of music you like or how you listen to it, so you are going ot have to use your judgement when you look at different systems, keeping in mind the people who sell them usually think more power and louder always = better. (Unfortnately it also = more $$.)
If you don't listen to music especially loud, a system with as little as 10w per channel is fine, and unless you really like to feel bass you don't need a subwoofer. You could probably get away with a head unit (the thing in the dashboard) that has an amplifier already attached to it, as opposed to better systems which have separate amplifiers that get mounted in the trunk or under the seat.