Windows 7: what does this features means

what does this mean and which of them is the most important thing too look at when buying a graphics card

Core Clock 650mhz
Shader Clock 650mhz
Memory Clock 900mhz
Memory Bandwidth 28.8gb/sec
GFLOPS 624GFLOPS
Pixel Fill Rate 5200Mpixels/sec
Texture Fill Rate 15600MTexels/sec
Memory Type GDDR3
Memory Bus Type (64x2) 128bit
Process 40nm
Shader Processors 480
Texture Units 24
Raster Operators 8

pls explain