I too am like the original poster asked wondering what to do with the lisence key generated by the developer console on my way to publishing in the Google Play store.
While all the above posts show how to export and create keystore etc in Eclipse or from a command line, none of them answer what the dadgum key Google offers up is for. Do I need to add it somehow? I see no way to specify the key Google generated as a "licening key" in the Google Play Developer Console, and NOTHING tells me HOW to bind THAT key to my app.
I already know how to export a signed app using eclipse but that does not have the Google Play key. If someone can point me in the right direction it is much appreciated.
OK I have figured it out. The licence key is irrelevant to signing your app and is for licensing purposes within your app.