benchmarks are to test graphics on various conditions, usually for gamers.
I.e The newest cards which are insanely pricey can do the latest games, Battlefield 3, on the maximum resolution, with Antialiasing and all details turned all the way up at amazing frames per second. thats what a benchmark tests. There are benchmarks for CPUs as well. Benchmarks test different components under the same conditions.
It depends on what you want.
For video enthusiasts, watching High res Movies, This is a good card for them
http://www.newegg.com/Product/Product.aspx?Item=N82E16814130632
For Gamers, Heres the best bang for your buck at the moment. All others pretty pricey, albeit more powerful
http://www.newegg.com/Product/Product.aspx?Item=N82E16814125401
Of course your motherboard would need at least one PCIe express slot. For gamers youd need a decent quad core, 4 GB of RAM, and a motherboard with PCIe Express x16 2.1 slots for the graphics.
But for movie enthusiasts, all you need is a PCI express slot on your motherboard and a decent dual core and your good.
Unless you have a laptop. Do you have a laptop? Because if you do, disregard everything here. you must buy a new laptop to upgrade anything on laptop.