How do i upload a an MP3 track from my harddrive to work on with Magix Music maker ?

I assume you are asking about MM-15, since you didn't say.  The easiest method is to use the File Manager at the bottom of the screen to locate the desired music file (MP3, WAV,etc.).  Simply double-click on the file and it will be imported automatically.  I assume you can also click and drag it into the arranger.