How Can I Get Heroku to Recognize My Application in my Filesystem?

I am new to Heroku, and I want to set up my simple Node.js app through Heroku. I have tried following the Heroku docs for setting up node apps, and I have done everything it says to do. Unfortunately I have gotten stuck on the Foreman/Procfile section. I have created a Procfile like the tutorial says (saved as a .txt file), and have put it in the same directory as my source files. When I try to run Foreman, it says "Error: Procfile doesn't exist". It makes some sense, as Heroku doesn't know where my app directory is, but I want to understand how I can fix this. Thanks!