I have no clue what any of you guys said really :|...I'm kinda a noob with computers. and I'm building a gaming rig.
It's marketing speak for the most part; these companies KNOW that a lot of people are easily confused with all these technical details, so they start yelling about GHz and Blast Processing and Hyperthreading until you give up and buy the more expensive thing they're recommending.
Don't worry, you can't really go wrong with any Radeon HD 7870. The biggest difference is different brands putting a different cooler on the graphics card, making some overclock a little better or run a little more quietly. Depending on what monitor(s) you'll be using, you may also want to check which connectors the card offers.