From the title of the post I assume that the instructions are in firebase?
You can take a look here, to use Web component with firebase:
METRIC RAT AI2 - Firebase with a Web Component
Here a tutorial about virtual screens:
How to use Virtual Screens - Tutorials and Guides - MIT App Inventor Community
or, if you prefer to use different real screens, you have here how to switch:
Switch screens correctly - 2 methods - Tutorials and Guides - MIT App Inventor Community
Some tutorials, resources and books to start with AI2:
Our Tutorials! (mit.edu)
App Inventor 2 Book: Create Your Own Android Apps
Course In A Box (appinventor.org)
And for sure, if you search in the community you will find a lot examples.