If you want to use Google Maps, you should get API key.
In template HTML files you should find google maps api js file. Example:
<script src="https://maps.googleapis.com/maps/api/js"></script>;
And add to this address your API key. Example:
<script src="https://maps.googleapis.com/maps/api/js?key=YOUR_API_KEY"></script>
How to generate API key see here - https://developers.google.com/maps/documentation/javascript/get-api-key#get-an-api-key