firebase facebook authenitaction

hi unity community

i am trying to add firebase authentication into my game, but the documentation in the firebase site is a bit confusing. i found this code on the unity forums:

 using System.Collections;
  using System.Collections.Generic;
  using UnityEngine;
  using Facebook.Unity;
  using Firebase.Auth;
  using UnityEngine.UI;
  
  public class facebookAuthenticator : MonoBehaviour
  {
      public Text userID;
      private FirebaseAuth facebookAuth;
  
      private void Awake()
      {
          if (!FB.IsInitialized)
              FB.Init();
          else
              FB.ActivateApp();
      }
  
      public void logIn()
      {
          FB.LogInWithReadPermissions(callback: onLogIn);
      }
  
      private void onLogIn(ILoginResult result)
      {
          if (FB.IsLoggedIn)
          {
              AccessToken tocken = AccessToken.CurrentAccessToken;
              userID.text = tocken.UserId;
              Credential credential = FacebookAuthProvider.GetCredential(tocken.TokenString);
          }
          else
              Debug.Log("log failed");
      }
  
      public void accessToken(Credential firebaseResult)
      {
          FirebaseAuth auth = FirebaseAuth.DefaultInstance;
  
          if (FB.IsLoggedIn)
              return;
  
          auth.SignInWithCredentialAsync(firebaseResult).ContinueWith(task =>
          {
              if (task.IsCanceled)
              {
                  Debug.LogError("SignInWithCredentialAsync was canceled.");
                  return;
              }
              if (task.IsFaulted)
              {
                  Debug.LogError("SignInWithCredentialAsync encountered an error: " + task.Exception);
                  return;
              }
  
              FirebaseUser newUser = task.Result;
              Debug.LogFormat("User signed in successfully: {0} ({1})",
                  newUser.DisplayName, newUser.UserId);
          });
      }
  
  }

by all accounts on the feed, the code works. however, i do not understand how i would invoke this in my game? how can i get users to fill in their info and pass it to this? do i need a button saying "sign in with facebook" and link it to this script? thanks