Google it if u dont know.
It is mainly used for tweaking like enabling supercharger,turboboost.
1. Stock Kernel
4. CWM Recovery
1. Download the zip and place it in a folder in your SD card.
2. Reboot into CWM Recovery
3. Install zip as a normal package
4. ZIP takes care of all other things
How to check whether it is working or not?
Navigate to " /data/local/tmp/ " you will see a file named init.d_log_test.txt, if that file exists open it up and there would be something written in it,that means u now have init.d support on stock ROM's.