15. The method as claimed in claim 14 , further comprising registering the user command according to a similarity between a text for the user command and a text for a spoken voice in response to the spoken voice for the user command being input in a state in which the audio for the user command is output.
14. The method as claimed in claim 11 , wherein the providing of the registration suitability determination for the user command includes providing a guide user interface (UI) guiding a registrable user command in response to the user command being determined to not be suitable for the registration, and an audio for the user command is output in response to the user command being determined to be suitable for the registration.