Guitar Hero 64 is a fictional game; there was no official Guitar Hero game released on the Nintendo 64. If it existed, it would have likely followed the rhythm game format seen in later Guitar Hero games, requiring players to mimic guitar playing to score points and progress through songs.  The Nintendo 64's hardware would have presented unique challenges in creating a game with accurate musical timing and button mapping, given its technological limitations compared to later gaming systems.

Guitar Hero 64

Grunty's Mansion 2.0