@amkhan you will have to understand the smali code only.....
you can convert the .class files after extracting to .apk files using JAD (java decompiler) but then, all the dependencies will be lost so you wont be able to recompile from that (you can but that tougher)
hope this helps....
Also, Please don't make another post, asking me to teach you
as, teaching anything via web is damn difficult and I don't have to time to teach you too...
busy with exams and placements
Regards,
M4Master