using matlab for speech to text(STT)

With the help of matlab want to write code for speech to text conversion. The method which I am using is by phenome concatenation. I am using spectrogram command,but not able to read/understand/use the spectrogram in such a way that can help in separartion/recognition of phenomes.

Googled about spectrogram but not able to get clear understanding about it.

so please guide regarding the spectrogram and its application for phenome recognition.

If any other approach is more suitable for STT, that will be also welcomed.

Thanking in advance.