For getting the practical view of converting .apk file into .java files just check out https://www.youtube.com/watch?v=-AX4NYE-9V8 video . you will get more benefited and understand clearly. It clearly demonstrates the steps you required if you are using mac OS.
The basic requirement for getting this done.
1. http://code.google.com/p/dex2jar/
2. http://jd.benow.ca/
