How to get google login API?

Hey can anyone help me get the google login api correctly for my website? i tried getting directly from here (https://developers.google.com/identity/sign-in/web/sign-in). After hitting the configure a project button and completing the steps i got client ID and client secret. I kept that the ids to my php theme and it didn't worked. I also tried clearing cache memory of my browser and the error is: here