1.Go to Setup-Options-Tick Shaders
2.Its used to get reflective floor,blood to stay and to make your toribash look better
3.A pretty decent Graphics Card that can run most games on high settings
4.Shaders got created in version 3.6-9ish (correct me) probably the latest version
5.No not all some outdated computers and laptops have old graphics card I suggest you update them but im warning you that upgrading them would cost alot and its too complicated especially on laptops
All new Video Cards support pixel shading 4, means you can run shaders.
But if you want to run them with ray-tracing, get a much more powerful card.
I have a 2x GeFore 8600GT SLi 512mb
All settings enabled and i have a 26FPS framerate out of 30.