Insert the audio adapter to the guitar amplifier's "Input" plug for use with the electric guitar or to the guitar amplifier's "Phones" plug for use with a headphone.
Insert one end of the guitar cable's jack to the audio adapter's mini plug for use with the electric guitar or insert the headphone's jack for use with the headphone.
Turn on the guitar amplifier and check the audio adapter. The sound of the electric guitar should be heard from the guitar amplifier when the guitar's strings are strummed. A sound should also be heard on the headphones if the audio adapter is used for headphones.