Download the following files.
- Put recovery-clockwork-touch-184.108.40.206-galaxys2.zip in the external_sd of your device.
- Put CWM-SuperSU-v0.97 in the sdcard (inbuilt) of your device.
- Power off your phone.
- Boot into Recovery Mode by holding Volume Up+Home Button+Power Button till you see the Android dude and then the list of options.
- Now using the Volume Down button scroll down to 'apply update from external storage' and then press the Power button to select that option.
- Select recovery-clockwork-touch-220.127.116.11-galaxys2.zip and let it finish installing.
- Wait for CWM Recovery to appear. From here on you will be able to use the touch screen so don't press the volume keys to scroll.
- Select 'install zip from sdcard' and look for CWM-SuperSU-v0.97 on your sdcard and install it.
- Reboot phone.
- Congratulations, your phone is now rooted!!
- Open Google Play Store.
- Find BusyBox (free) and install it. Open the app and install BusyBox.
- All Done!