To create amusic track or background audio for video in Movie Edit Pro (MEP) this is better done in Music Maker (MMM) and exported as WAV or MP3 for use in MEP.
To create a soundtrack synchronised to the movie do the following:
Create the movie in MEP and export as MXV file - File, Export movie, Video as Magix video - I would suggest a resolution no higher than 1920 x 1080.
Import the MXV file exported into MMM onto track 1 and turn on the video monitor
Create the sound track and save the project you may need to return to it.
Mute the video track in MMM then export the sound track as WAV or MP3 from MMM and import it into the movie in MEP.
To do this manually in MEP is very time consuming and can be frustrating.
You can use Soundpool loops directly in MEP, but I suggest that you first make a copy and use the copy because MEP will create temporary files in the folder, something you want to avoid in the main Soundpools folders.
Another way to do what John EB suggested is to use the Share method. See 9:39 in this tutorial:
or follow this tutorial done in 2015 and the method has not changed, just the programs: