Do you have your music on your computer in a place you can find it?
Is it in .mp3 or .wma files? (Not iTunes files, m4a or m4p or aac.)
Then you don’t need WMP. You can just drag and drop them onto the unit or a microSD card in the slot.
On the unit, go to Settings/System Settings/USB Mode and change it to MSC.
Connect the Sansa. Open the driveletter that says Sansa Fuze or the one after it that says Removable Disc.
Copy-and-paste your music files onto the driveletter or, if you prefer, into the Music folder or any folder you want to make. Done.
Meanwhile, if they are iTunes files, then go into iTunes, go to the album, highlight all the files, right-click and choose Create mp3 version. Then find the mp3 files on your computer and copy-and-paste them over.