1. Open the site that you want to customize trough Site builder.
2. Drag and drop "Google Maps" icon to add it to the relevant location on your page.
3. Resize it to the desired shape to fit on your site.
4. Open the settings panel - you have to press on "Properties" button either by clicking on pencil icon (-top right corner of the google maps box) or right-click with the mouse on the box.
5. Open in new tab https://developers.google.com/maps/documentation/javascript/get-api-key and click "GET A KEY".
6. "Enter new project name" - specify name ("mysite" for example) and agree with Terms of Service.
7. Click on "CREATE AND ENABLE API" button.
8. Copy YOUR API KEY.
9. Go back to Site builder and paste the key in the field below "API Key".
10. You can select Address by typing it or to drag the marker on the map below.
11. Select "Zoom level".
12. Click "Apply".

Check out the video for a better visualization of Google maps integration: