Bit too broad of a question. I would do as suggested and google it. No shortage of literature online. If your interested in VMWare specifically (VMWare does pretty much own the market now but is not the only option. Microsoft, Xen etc..) their webpage offers plenty of documentation.
Been in the ESX/Virtual Infrastructure world for about 3 years. If you have any specific questions feel free to ask them. Be happy to answer them if I can.
In general, you have a host OS. Perhaps you want to run VMWare Workstation or Server on your windows box. Or the enterprise version would be ESX server, which is basically a scaled down version of the Linux Kernel at the console with VMWares VMKernel conrolling the virtual environment. You would then create VM's as "guests" on the host machine. Fundamentally, VM's are flat disk files, .vmdk's, with vmx configuration files that control configuration parameters. In the VM, its no different to you than a physical box would be.
That's a rough generality but hopefully you get the idea. Ask if you have detailed queries.