You can add tracks to a Spotify playlist and send notifications to followers when the track is added or removed from the playlist. The application uses FastAPI for building APIs and Twilio SendGrid for sending emails. It also utilizes the Spotify API for authorizing access to playlists and tracks. The email_notifier.py file contains code for creating APIs and sending emails via SendGrid, while the spotify_authorization.py file handles user authorization with Spotify. The application can be run locally or exposed to the internet using ngrok. When a user authorizes access to their playlist, they are redirected back to the FastAPI app with an authorization code, which is then exchanged for an access token that is used to add and remove tracks from the playlist.