Is it possible on (10.2.0) to alter the volume of a track is a specific area only? New User:-) . Is there documentation available to tell me how to do this?

Hi GarageBand users - I wish to alter some MP3 backing tracks for use with my duo. I'm running a Mac Mini with GarageBand V 10.2.0. I'd very much like to alter the volume of 'specific areas' on a single track. I can insert the MP3 into GarageBand and alter the volume or EQ for the whole track but I'm struggling to find tools that will allow me to define an area on a track and just alter the volume for that bit. Can anyone tell me how to do it or point me in the direction of some documentation that will:

1. Tell me how to define area(s) / section(s) on a track to enable editing?

2. Tell me how to alter the volume in a specific area / section of a track?

Many thanks for looking.