Oracle VirtualBox is virtualization software that can host a variety of operating systems. It does not include the Microsoft Windows operating system, which you would need to purchase and install separately. In that regard it is very much like Boot Camp, which enables a Mac to boot and run Windows natively. I surmise if you installed Windows in Boot Camp you can also install it in VirtualBox without having to pay for another copy, but you would need to check Microsoft's licensing restrictions for a definitive answer.
I do not know how much memory is required to run Windows, but if you have it installed and running using Boot Camp then obviously your Mac already has sufficient RAM.
Once installed in VirtualBox, you will effectively have a Windows PC, and can do anything with it you could otherwise do with a PC. Windows will just run slower than it would natively as it does using Boot Camp. The only advantage is that you don't have to reboot to switch from one operating system to another.