Old console games can be played on computer through the use of an emulator program. The game itself being a ROM file, with appropriate file endings depending on the system it's coming from, for Sega Genesis / Mega Drive (European name) it's usually
.md.
Here's a list of downloadable emulators for Sega Genesis, I've been personally using years ago Gens, which I'd probably recommend -
link.
As for the game ROMs, the use of them on computer through emulation is a gray area at best, illegal at worst, so I can't provide directions where to get them from. However there should be still many sites offering them, it's just a quick Google search.