To write disks, you need this cable: it connects the parallel port to the FDS RAM adapter.
you also need a disk copying software FDS file...Disk Keeper, disk copier, etc. You choose. I can't point you to one, but Google if your friend. http://www.tototek.com/store/index.php?main_page=product_info&cPath=1_35&products_id=98
Then you need to check your Power board doesn't need to be modified, if it does use this guide:http://famicomworld.com/workshop/tech/fds-power-board-modifications/
Check your drive doesn't house the FD3206 chip, and if it does, mod it, or get a different drive if possible.http://famicomworld.com/workshop/tech/famicom-disk-system-fd3206-write-mod/
Make sure your compy is suitably old and can run DOS
and follow the attached guide to make disk images writable to FDS
One more thing....if the disk you are using has more than one side...change the last hex digit of the FDS header to '02' instead of '01'.
Hope this helps! I've been able to write disks on my drive that work with no issues on other machines, but your results may vary.