Lot of confusion on using Google sign in authentication

If you want an answer, other than a link to one of those tutorials, you'll need to provide more detail.

Click "Improve Question". Show what you've actually tried (code-wise) in "What I have tried". Don't simply repeat your description.

Clearly, you didn't get the expected result. So, something must have gone wrong. Improve your description to clue us into what happened. Did you get a compile error? If so, what was it? Did you get a runtime error? If so, what was it? Did you observe a behavior you didn't expect? If so, what was it?

We can't see your screen. So, without this information, all we can do is take guesses or post a link.