Hi,
As explained on the link on the marketplace, you'll be using these with this plugin:
Geocoding API, Places API and Maps JavaScript API
You can see on your link that geocoding is 5$ per 1000 requests, and maps javascript API is 7$ per 1000 requests, with the first 200$ free each month.
So basically, you can geolocate about a few thousands addresses for free each month.
Note that the address is only geolocated when it's created or modified.
So basically, you'll pay nothing to use the APIs from Google unless you have a big store with thousands of new/modified addresses each month.
You'll see in your Google Maps account statistics about your usage of the APIs and how much it will cost and what you'll have to pay on that.