Visual Studio Connection 2019 c# with Firebase

Question

I tried for hours and even days to look for application examples for VS 2019 connection extensions (in C#) with Firebase, but without any success. I feel that almost nobody uses it for lack of more detailed information.

I downloaded the extensions Firebaseuthentication.net, Firebasedatabase.net and also Firesharp in Visual Studio, but the documentation is very superficial and I’m not being able to use it.

Example:

1. Send and search user authentication information with e-mail and password
2. Access nodes and your children for reading and writing.
3. What does it mean .StartAt(???) .LimitToFirst(???) .OnceAsync(); (of FirebaseDatabase.net)
4. Main properties of each using necessary.
5. How to search and send the command push of id single by Firebase.

Example:

var firebase = new Firebase
    .Database
    .FirebaseClient("https://fir-app-20502.firebaseio.com/");    
var idUser = await firebase
    .Child("CSharp")
    .OrderByKey()
    .StartAt(???)
    .LimitToFirst(???)
    .OnceAsync<???>();

I’ve been watching some Indian video about Firesharp, but there’s nothing about authentication.