I can't figure out .FDS

I Googled, but couldn’t find anything on how to run a .fds file. I generally load content and select core. Don’t have a playlist, haven’t scanned any folders. One thing I read was put the BIOS into the same folder and that didn’t work (it was actually for Android, I’m on PC), and a lot of the results are either Retropie or from older and more complicated builds of Retroarch. Tried loading the BIOS and it let me choose a core and then failed, but the .fds fails without that option.

bios should be names disksys.rom, place this whichever you set your folder to be

then just load roms normally with nestopia/fceumm

fceumm supports .fds with out without header, not sure of nestopia.