with what Magix software are you trying to use it and what do you want to do ?

Have you connected it (correctly) to your soundcard  / headphone & mic input ?

Does your headphone/mic set work with any other programs ?

If you are using MM16 activate the Audio Rec button at the left of the track and then hit the red record button on the transport control (next to play pause stop etc) another window will open to start recording. make sure you mic is selected as the input device (check the record level meters move when you talk or sing) when you are ready hit the red button to start record and then hit stop when you have finished - you will then be asked if you want to keep the take click yes and it will appear as an audio track on the timeline .... simples !!