To create an API key for Google Maps, visit Google's API Console at https://code.google.com/apis/console and log in with your Google Account. Create a new project.
Click then "APIs AND SERVICES" -> "Library" and activate the "Google Maps JavaScript API" and the "Geocoding API".
Next, click "Create Credentials" and choose "API key". The API key will be created then.
By default a key can be used on any site. We recommend to restrict the use of your key to domains you administer only. This prevents unauthorized usage on other sites. You can specify which domains are allowed to use your API key by clicking the Edit allowed referrers... link for your key.
Copy the key to Google Maps API Key in the VIMP backend at Administration -> Configuration -> Google Maps. Google Maps is being activated for users and media per default afterwards.