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)
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