As others have done with their blog, I plan to use this as a repository of things I learn, not a “I’m a ninja on this topic, read this to learn everything!”, quite the opposite actually.

Testing android app, get the .apk file, simply download it onto the device and double click the file to install it. Once the file installs, it will be runnable.

To open an .apk file, change the extension to .zip and unzip it. That will include manifests, xml files of information and dex file(s), which is the actual java code that can be decompiled with something like dex2jar (included in Mobisec). Then simply use JD-GUI to read the class files!