This module provides the ability to convert address field values into a set of coordinates that are stored with the entity. This enables the content to be found in search based on location.
OpenStreetMap
By default this module uses the OpenStreetMap API. It is not needed to enter an API key.
You can find the usage policy here: https://wiki.openstreetmap.org/wiki/API_usage_policy
Google Maps API Key
Optionally you can use the Google Maps API to transform address strings into lattitude/longtitude pairs. For all server side requests no Google Maps API key is needed, however, rate limiting may apply. For the client side requests which include the proximity filter and map blocks, a valid maps API key must be entered on the geolocation's configuration page.
You can generate a key here: https://console.cloud.google.com/google/maps-apis/api-list?project=social-local-171213&organizationId=841499249988
Configuring your own Address fields to store geolocation data
You can simply enable the field_ui module
See step "Geocoding results from Address field": https://www.drupal.org/docs/8/modules/geolocation-field/configuring-integration-between-geolocation-and-address-field
And it should store your Address data in geolocation fields as well.