Generally when you want to install an app on the Kindle from Google play what you do is download it to another android device, in my case my cell phone. Then you use a file manager, in my case ES File Expert to back up that app. Once you connect the phone as a storage device via usb to your pc, you can copy that appname.apk to another folder on your hard drive. You then can connect the kindle fire as a storage device via usb, and copy that .apk to the kindle. From there your file manager (ES File Expert is available in the Kindle store) can install the desired app from backup.
The first time you do this it's rather laborious. However once you've done it the first time you can then use the same folders and process for other apps. I installed dropbox as the very first app then created a folder in dropbox to hold the .apks. I can then just copy them from the android cell to my dropbox folder and restore from same on the kindle, bypassing the pc altogether.
Note, this means you can load apps on the kindle not approved by amazon. This also means you can load apps not designed for the kindle, not guarenteed to run on the kindle, and in a possible worst case, damaging to the kindle. As with all such, proceed at your own risk.
