Is it possible to read an audio signal using the audio jack as my sound interface?

I am trying to display the sound level from my microphone. I have tried the sample code from matlab. It doesn't work. I am thinking I need a microphone with usb connection. How can I access the audio port using the audio jack as my sound interface?

[Star Strider]

What does ‘it doesn’t work’ mean?

• What does it do that it shouldn’t?
• What doesn’t it do that it should?

[David Dijemeni]

The code doesn't get the sound level as code is might to