I'm looking at an album I downloaded from Amazon. The album is "The Seekers - Farewell (Live)", the artist is "The Seekers".
When I downloaded the album, Amazon provided a ZIP file that I named "AmazonMusic-TheSeekers-Farewell_MP3.zip" on my hard drive. (Amazon might have wanted to call it something less helpful, but the POINT is that it was a ZIP file.)
When I unzip this ZIP file -- Windows 10 will unzip these, you don't need any extra software -- I get a directory on my hard drive that is named "The Seekers". That directory contains a directory named "The Seekers - Farewell (Live)". THAT directory contains 22 mp3 files, numbered 01 through 22, with the names of the songs.
To import this downloaded album to my B2, I must retain the "Artist\Album\tracks" directory structure on my USB stick. In other words, on the USB stick, I need a directory named "The Seekers", containing a directory named "The Seekers - Farewell (Live)", containing the tracks.
Daniel suggested having a top level directory named "music" ABOVE the artist directory; that won't hurt. Some people have found it necessary.
If your USB stick is organized ANY OTHER WAY it can cause problems with the import.