Best Buy is about the WORST place to have an install done.
You need to find a wiring harness for you vehicle. Basically this is how it works:
Your vehicle comes with a harness already, it is hard wired into the engine harness/vehicle computer/electrical system. To prevent you from having to splice your unit directly into this, you can buy a "go-between" harness that will mate your vehicle's wiring and the wiring of your unit together painlessly.
Does your car have steering wheel controls? If so, you can buy an adapter from PAC that will allow you to use your steering wheel controls with the headunit. These come with great instructions on how to install.
If you're going to do the install yourself, get a digital multimeter and the factory service manual for your car (you can usually find these for free around the net if you know where to look). You need the service manual for wiring diagrams.