EIHadi,

Magix doesn't use the term 'ducking' but rather the application of a 'volume curve'. Right click on an audio track and you should see it as a menu option:

The curve will appear on the track and you can click anywhere to create a dragable point and adjust the levels as needed. If you go to 'Effects' >> 'Audio effects' you will see that a keyframe animation has been created for this object's volume.

Regards,

Carl