This is EXPERIMENTAL beta software. It contains many remaining bugs!
If you want to contribute, fork it and do a pull request on Github: https://github.com/dschuermann/openpgp-keychain
Install K-9 Mail for the best integration, it supports APG for PGP/INLINE and lets you directly encrypt/decrypt emails.
It is recommended that you install OI File Manager to be able to use the browse button for file selection in APG.
First you need some keys. Either import them via the option menus in "Manage Keys" and "My Keys" or create them in "My Keys".
Please report it in the issue tracker of OpenPGP Keychain.