Foreman: Command "start" is not defined

I'm getting the above error when trying to run foreman start from command line.

I installed the gem:

gem install foreman

Then defined a procfile. Why am I getting this error? When I run foreman list, I get:

Available commands:
  build         Commission Forman to build a new Laravel app for you
  help          Displays help for a command
  list          Lists commands
  scaffold      Generate a scaffolded Foreman template file
  self-update   Updates the application.