In order to build an app identical to the live demo, you need to populate Firestore with data.
Populate your Database with Quiz Data
I recommend cloning the Quiz Questions Repo. It is a node script that allows you to populate all the quiz data in your own database with a single command.
Database Model
You can also create your own data from scratch. Below you will find screenshots of sample quiz data for each collection.
Topics
Topics collection data model
Quizzes
Quiz collection data model
User Report
Report collection data model