Quick examples:
WinUAE (amiga)
Majority of Playstation 1 emulators
PCSX2 (ps2)
PC-Engine emulators
Sega CD
Just run the emulator, if it needs a bios it will ask you to select/configure it.
Also quick note, some emulators may ask for a bios optionally. Meaning, they will run without one but for better compatibility you can use it. Can't remember of one right now but they do exist.