Download the .apk to your device and install it. You can always find the latest instructions here: https://www.humblebundle.com/app
If you need help with .apk files, check out the first few steps of our video for installing Humble Bundle for Android games:
http://www.youtube.com/watch?v=6dYWFYqz2j4Activate the app by logging in to your Humble Bundle Account. If you have not created an account (even if you have purchased in the past), please do so at https://www.humblebundle.com/signup. Open the Humble Bundle app on your device. Tap on "Log In" and enter in your email and password to your Humble Bundle account.
Filling out the form below is not required, but please do let us know if you discover any bugs, or have specific feedback. Thanks for your help!