Emulators
Emulators are programs made to emulate certain consoles that would otherwise cost alot of money to play. They are cheaper alternatives towards playing a game on a console. In order to play most games from consoles, you would need an emulator.
These are the most common N64 Emulators: Project64, Mupen64 and Bizhawk
What are the differences between the emulators?
Project64 is most commonly used to support Super Mario 64 ROM hacks, as well as having the feature to use cheats on all ROMs.
Mupen64 is most commonly used for recording movies, making TAS'es and testing purposes.
Bizhawk is a multi-emulator program that supports all types of consoles, including N64, Bizhawk is also used for making TAS'es, but Mupen64 is more commonly used.