what is the difference between VGA & AGP card?

That's kind of like asking, "What is the difference between a bicycle with a black tire and a bicycle with a high-rise handlebar?". You could have a bicycle with either one and not the other, or you could have a bicycle with both, or you could have a bicycle with neither.

In this context, the "VGA" connector is that little 15-pin "D-Sub" socket on the rear of most of our computers to which we connect our monitors. There are other connectors that are sometimes used, but I think this is the most common.

"AGP" refers to the bus and the connector on some motherboards where we plug in our video cards. (Some motherboards may have built-in video circuitry that has the same characterstics as an external AGP video card.) Nowadays fewer and fewer new motherboards are being released with AGP video bus, and PCI-Express is becoming ubiquitous.



References:

http://en.wikipedia.org/wiki/VGA
http://en.wikipedia.org/wiki/Accelerated_Graphics_Port
http://en.wikipedia.org/wiki/PCI_Express

Regards,

Dave