A software engineer built a mobile app that uses Twilio's WhatsApp API to discover indigenous groups and territories near users' locations. The app utilizes Native Land Digital's API, which provides information on recognized territories across North America and the world. To build the app, users need a free Twilio account, a phone number, and a personal phone number. They also need to set up a Twilio Function using the node-fetch module and configure it to respond with messages containing information on indigenous groups near the user's location. The process involves creating a Twilio Function, setting up a WhatsApp Sandbox, and deploying the function. Once complete, users can send their location through WhatsApp to receive information on indigenous groups in their area.