The app is using amplify to manage the backend. Get Started with amplify here
Behind Amplify Authentication (User Pools) and Authorization (Identity Pools) AWS Cognito is used and can be tweaked in some cases.
You can redirect users to the app from a website or another app using deep linking.
The routes are defined in src/navigation/index.tsx
To open the app with route params you can use uri-scheme package as follow:
npx uri-scheme open instagramclone://comments --android
npx uri-scheme open instagramclone://comments --ios