I downloaded it to my Kindle fire. How do I start using it?
You have downloaded a Windows application and try to run it on a different operating system (Android). This operation won't be possible unless you have an emulator, which doesn't exist at this time. I recommend getting a dedicated screen recorder using the Play Store application available on your Kindle Fire.
You can either open Play Store then type screen recorder or visit the following URL which will display all the apps related to screen recording: https://play.google.com/store/search?q=screen%20recorder