Existing webseite template in rails

I'm new to ruby on rails and asking myself how I can build up a ruby on rails project on my existing template that is a collection of html, css and js files? is that even possible or do I have to start a ruby project from scratch and write the html for my template another time?

I managed to show the template by putting all the html files in public/ folder but I get the feeling that this not how it's intended to be.