You can test how this functionality works for any address, this demo is provided by Google: https://developers.google.com/maps/documentation/javascript/examples/places-autocomplete-addressform

1) You need to get API Key from Google. Google Maps JavaScript APIalso needs to be enabled for that key. Google provides the service and the key for it so you need to get it yourself, I cannot get it for you.

a) Go to https://console.developers.google.com/apis/credentials?project=x2-double-gamma-k

b) Click button "Create credentials -> API key" (copy the API key, you will need it later)

c) Click colorful link at top left "Google APIs" -> go to "Google Maps JavaScript API" , enable this api

d) Activate the Google Places API Web Service

e) Enter the api key in Magento backend System>Configuration>Sales>OneStepCheckout>Google Places Address Autocomplete Setup>Google api key

In case Google Places is not working in One Step Checkout, please go through the following list and double check everything.

Please check the following 2 things :

2) Usually the issue is that region field is "excluded" in System>Configuration>Sales>OneStepCheckout>

If it is excluded, please enable and test again