Step 1: Login to Google Developer Console at https://console.developers.google.com using your Google account credentials.
Step 2: If you are not registered on Google developer account, then you need to accept agreement and fill out detail to register an Google Developer account
Step 3: After accepting agreement or if you are already registered on Google developer account, you will see a screen as shown below. Click on “Select a project” on top header bar.
Step 4: From the project selection popup click on the button Add new project. Enter your “Project name” and click on “Create” button.
Step 5: Back to main console dashboard, select your new project. Go to Credentials > Create credentials click OAuth client ID
Step 6: Select Web application > Click Configure consent screen
Step 7: Fill values for some textfields to complete creating credentials like image bellow.
Step 8: After creating credentials successfully you will get a client id. Copy Google App Client ID