Is the USB device a memory stick/pen/thumb drive or a USB hard drive? If a drive, it needs to be powered from a power adaptor, not just USB power.
In the case of memory sticks there are often odd features on the sticks which initially make them unsuitable for DJ use such as encryption, the drive presenting itself as two drive letters rather than just one, bloatware, backup utilities , splashscreens and start-up menus etc The drive itself or the manufacturers website often features a program to remove all that fluff.
Music manager software needed the files to be in folders no larger than 1000 loose tracks per folder
From a. completely empty drive
Put the tracks/folder on the drive
Plug the drive into a computer which has music manager on it
In music manager point to the drive with the music on it
Choose menu option for "create database"
Let it run until complete
When adding more files later
Put the tracks/folder on the drive
Plug the drive into a computer which has music manager on it
In music manager point to the new folder(s) with the music on it(them)
Choose menu option of "add to database"
Let it complete
