If you plan to use the built-in tile sources that are supported by the C1Maps control, you first need to get a Bing Maps Key. You can go to the Bing Maps Account Center to create an account and get a key.

http://www.bingmapsportal.com/

For more information on obtaining a key, visit the Microsoft documentation below.

http://msdn.microsoft.com/en-us/library/ff428642.aspx