Best Buy is a poor place to learn about stuff. And also a poor place to purchase this stuff. Strangers on the internet are not likely to do your shopping for you. List stuff to buy at BB? That's your job.

Here's some help:
You need 5 regular speakers and 1 subwoofer for 5.1. You need only 1 receiver. Speakers are most important to sound quality, but the receiver matters, too. Listen to speaker systems in your price range to find what you like. It's true that most in-the-box products are poorer in quality than separate purchases. But that's not always true. Some better stores will combine a nice speaker package with a nice receiver for a lowered price.