Login to your Gmail Account and Start with here
1. Create New Project as shown below :
2. Enter desired Project Name, to get access to a new project and click on Create :
3. Notification of Newly Created Project.
4. Click on ENABLE APIS AND SERVICES.
5. Search for APIs and Services to Enable Google Drive API.
6. Click on Enable.
7. Click on APIs and Services.
8. Go to Library.
9. Enable Google Sheets API.
10. Click on Enable.
11. Again Click on APIs & Services.
12. Click on OAuth Consent Screen.
13. Select External as User Type and click on Create.
14. Enter the desired Application name and Save Credentials.
15. Click on Save and Continue.
16. Click on Save and Continue.
17. Click on BACK TO DASHBOARD.
18. Click on PUBLISH APP
19. Click on Create Credentials to obtain new credentials.
20. Click on OAuth client ID.
21. Select Web application in Application Type and click on create.
22. Your Credentials have been generated.
23. Copy and Paste credentials in respective fields and Generate Client Token by clicking the button “Click here to generate an authentication token.” allowing access and pasting the code within the Client Token field.
Note: Client Token will only allow you to create if you have already added Client ID and Client Secret Keys with the above fields.