I am not computer literate so please explain in a simple way.
I have installed Microsofts Flight simulator but my computer says I must have "geForce3Radeon8500" class or better.
What is this?
About how much does it cost?
Can I install it myself?
Thanks.

It's a graphics card. Probably cost in the $100-S150 range and you should be able to install it yourself.

The card you can install depends on the computer you have and the type of video card slot (if any) that it has.