Windows 10 Pro (and Enterprise) includes Hyper-V and all the ancillary software (drivers and such) you need to run a virtual machine inside Windows. If you have only the regular version of Windows 10, you need to look elsewhere. (Hint: Use Google, and find a copy of VirtualBox.)
In addition, to get the Hyper-V program going, you must be running the 64-bit version of Windows 10 Pro, with at least 2GB of memory. The hardware itself must be fairly up to date because it must support the Second Level Address Translation (SLAT) capability. You can find a good overview of testing for SLAT on the How-To Geek site.
Why would you want to use a VM? Many reasons:
- Suppose you have an old program that runs only under Windows XP or Windows 95 (or even DOS, for that matter). You set up a VM, install XP or 95 (or DOS), and then stick the old program inside the VM. The old program doesn't know any better — it's fat, dumb, and happy working inside of XP. But you're watching from the outside. You can interact with the old program, type inside it, click inside it, give it disk space to play with, or attach it to a network interface card. A fake (virtual) one, of course, that works just like the real thing.
- You want to try a different operating system. Maybe you want to play with Linux for a while or take Windows Server 2012 for a ride. Or you get nostalgic for the days of Windows Me. Or Microsoft Bob. Set up a virtual machine for each of the operating systems, and install the operating system in the VM. Then close each VM and save it. When you want to play with one of the OSs, just crank up the right VM, and you're on your way.
- You need to isolate your real system while you try something that's tricky or experimental or potentially dangerous. If you have a VM that gets infected with a virus, the virus doesn't necessarily spread to your main machine. If you try a weird program inside a VM and it crashes, restarting the VM is much easier than restarting your PC, and if there are any bizarre side effects — say, weird Registry changes — they won't affect your main machine.