Can someone help me understand what is the root of my application?

I would like to use vim and create a one line procfile in the root of my application.

Then I can test the procfile using a gem called foreman with the following command in my terminal: foreman start

I have tried sudo vim /procfile and created the file and saved it in what I thought to be the root. Then I typed: foreman start and the response is that Procfile does not exist.

Any help would be most appreciated.