Simple explanation for using Docker to do Rails development on Windows (workflow etc)

Can someone please explain to me how to use Docker to do Rails development in a way that I’d understand and be vaguely familiar with? Ordinarily I’m used to firing up a virtual machine on my windows box to run Linux and do development work inside of that. After having to provision several different virtual machines on several different PC’s (and go through the same process of getting it set up for Rails development) I decided to investigate other options.

I decided to give Docker the nod over Vagrant which is often suggested, but I’m wondering if I’ve made a mistake? As I’m on Windows I can’t start Rails development, so I don’t begin with an app to containerise. Maybe I misunderstand, but I assumed Docker was basically a virtual machine running in the background and I could just use the terminal to set that all off manually.

All of the guides I’m reading seem to start with a Rails app already begun.

Any help, links, guides etc are greatly appreciated.