[Download][1] and copy the GAPPS zip file to your SD card. 

Reboot your phone into CWM recovery mode. To do this, turn phone off, and press Volume Up + Home + Power button together. Your phone would then startup into recovery mode.

Select `install zip`. Look for the gapps file via `choose zip from /sdcard` if it's in the internal sd card, or `choose zip from /storage/sdcard1` if it's in the external SD card.

After you flash it, reboot your phone (it's in one of the options).

  [1]: http://goo.im/gapps