Hi guys,
I want to make a sound file by recording with a music background
And to avoid to lower the level of music every time I record
I want to find an automatic method where the music level gets reduced every time I record and returns to its normal level if I am not recording
Can I do that with Audacity?
Thanks in advance 
Audacity does not apply effects during recording. It only applies effects to tracks, or parts of tracks, that exist in the project.
If you have recorded or imported an audio track into the Audacity project, and you have recorded your voice as a separate audio track, then you can use the Auto Duck effect to reduce the level of the music whenever your voice appears on the voice track. See: http://manual.audacityteam.org/man/auto_duck.html