flutter developer have knowledge with real time firebasedatabase

this is not a project and I'm new to flutter and practicing with course i bought it from website, any way i want to add new features like search in data base for specific user by email and and if the user email is exist so we going to click on it and add to the fav list and we need to show name , email and phone number of that user.
if you interest in this. you add comments on the code because this will help me to learn .