To build and run a project, use
stack run
from the project directory. This will download all the necessary dependencies, compile the project and start CodeWorld canvas server on address http://localhost:3000.
Add new files to the src directory. Pay attention to the naming — start your files with upper case letter and name the modules with the same names as the files.
To use replace the main entrypoint, alter the app/Main.hs file to import the required module and run the required IO () function.