Bing Maps geocoding library
To be able to use Bing Maps geocoding library on your site you will to get an API key. First you need to sign up (or sign in if you already have an account) at Bing Maps development center. You may do so at the following URL:
Once signed up, create a new key. Make sure to set the value of Key type to Basic and Application type to Public.
Now make a note of your new API key.
Now go back to Bing Maps settings page on your site and fill in your API key in the appropriate text box.