The app is completely anonymous. This is not contact tracing. The app uses a specific Bluetooth feature on your smartphone to detect phones nearby with the same feature enabled, however your location and identity are always unknown. Both phones exchange random IDs with each other that change frequently.
The random IDs your phone collects are stored in an exposure log for 14 days. This exposure log allows the app to notify you if you may have been exposed to COVID-19. If you are diagnosed with COVID-19 you can choose to share your own device's random IDs with the app so it can notify others anonymously and encourage them to take action like getting tested or self-quarantining. We call this key intervention an anonymous exposure notification.