Oh, it’s just a tool that you use to run operating systems. The OS isn’t actually installed to your computer; it’s just the ISO file that’s on your computer. That ISO file has the code required to make the operating system work.
If you want to install an OS to your computer, you need to dual-boot and blah blah blah…
BUT installing the OS to your hard drive enables more features than if you run it using a virtual machine.
I use VirtualBox, it’s completely free (there isn’t any technical support from Oracle, the people who made it, but there’s a VirtualBox forum), and it’s pretty easy to use. Assuming you have some technical knowledge.
Also, if you want to run Windows in a virtual machine, you need a generic key. A generic key is used to install Windows but if you want to activate it, you need a product key. I don’t think you can use product keys on VirtualBox, but you might be able to. Product keys do cost money though.