The file directories, emulator and operating system will be different for everyone but here's a rough idea. You can probably add more file extensions under the romext part if the roms aren't compressed.
Windows 10
# Generated by Attract-Mode v2.4.1
#
executable C:\retroarch\retroarch.exe
args -L cores\mame_libretro.dll "[romfilename]"
rompath C:\retroarch\rom\
romext .zip
system Arcade
info_source listxml
artwork flyer
artwork marquee
artwork snap C:\retroarch\video
artwork wheel C:\retroarch\wheel
Linux, Manjaro
# Generated by Attract-Mode v2.6.1
#
executable retroarch
args -L $HOME/snap/retroarch/393/.config/retroarch/cores/mgba_libretro.so "[romfilename]"
rompath $HOME/Desktop/GAMES/gba
romext .zip
system Nintendo Game Boy Advance
info_source thegamesdb.net
artwork flyer
artwork marquee
artwork snap $HOME/Desktop/GAMES/gbavid
artwork wheel