Dictation is the new feature in the Mac OS X Mountain Lion and it does not come enabled by default in the OS, which is kind of weird. Fortunately, it is very easy to enable (or disable) and super easy to use too. Here is how to do it.
1) Go to system preferences and clock on “Dictation & Speech”.
2) On the ‘Dictation’ tab, click on radio box to enable this feature.
3) Choose ‘enable dictation’ from the confirmation dialog.
4) You require network connection for this feature to work so whatever you say is sent to Apple servers for conversion.
That is it, to use it, simple double tap on the ‘fn’ key to bring the dictation. Thanks to new technology for the tip!