iOS: Firebase Custom Authentication Setup (Node.js)

I've followed the links on the Firebase Website and have ended up with multiple different links open. (Links below)

I am trying to implement Firebase's Custom Authentication Feature for my iOS application. I have made a Custom Credential on the Google API Manager website, but the instructions do not give me clear instructions on how to use them.

In my xcode file I have written the following code for Sign In:

@IBAction func LoginDidTouch(sender: AnyObject) {
    FIRAuth.auth()?.signInWithCustomToken(customToken) { (user, error) in
        if error != nil {
            print("Incorrect")

        }
        else{
            print("LoggedIn!")
        }
}

As per what I understood from the Firebase instructions, I wrote the following code and saved it as Firebase Node.JS:

var firebase = require("firebase");

 firebase.initializeApp({
serviceAccount: "path/to/UzuApp-186f9a6b5406.json",
databaseURL: "https://uzuapp-a531a.firebaseio.com"
 });

I've written down all the links I have open in the Google Doc below: https://docs.google.com/document/d/13KhHPKDU-Lb3H1N0eWU2RrrxvrFCO5OurFDpvehBVe8/edit?usp=sharing

(Links are not necessarily open in that order. I also might be missing some links that I have open but I'm almost positive that is all of them.)

Any instruction on what I'm doing wrong and what I can do to fix it would be greatly appreciated!