Go to the Google Cloud Platform Console.
Select the project for which you want to add an API key.
Go to the CREDENTIALS page. (From the Navigation menu click APIS & SERVICES > CREDENTIALS.)
Click CREATE CREDENTIALS > API KEY.
The API KEY CREATED dialog displays your newly created API key.
Click RESTRICT KEY. (If you click CLOSE, you can still set up restrictions later.)
On the API KEY page, under KEY RESTRICTIONS, set the APPLICATION RESTRICTIONS.
Select HTTP REFERRERS (WEB SITES).
Add the referrers (follow the instructions).
Click SAVE. For more information, see Restricting an API key
Now copy your API credentials and login to your web website as a admin
From left menu navigation general click on settings page
on scroll down and find the google maps input to paste your API credentials and save the page.
Make sure you have white-listed your domain and URL else places API will not work
Watch fulle video on youtube from below link :