Step 1: Proceed to Google Cloud Console site.
Step 2: You need to create or select a project to get the API Keys. Create or select a project on which you want the API Keys to be.
Step 3: For a mobile site, click on the menu button on the left side and select Credentials. For desktop sites, just click Credentials as seen at the left-hand side of the screen.
Step 4: On the credential page, click on Create Credentials > Api Key
Your API Key should be written in the lined box. You can copy it. (Remember to restrict your keys to ‘Google calendar api’ to avoid unauthorized use).
Step 5: Click Close.
Step 6: You can view your API Key from the Credential page under API Keys.