Download RetroArch, a multi-emulator program, then install a N64 core, I believe it's called Mupen64Plus. Configure the emulator's controls to your liking.
I would recommend Project64 which is the emulator I grew up and I'm most familiar with, but the devs have turned it into nagware now (the donation message you get every time you open it becomes more and more annoying each time) and I forgot which was the last decent version. Something like 1.7 I think.
Step 2 is finding the game. I recommend getting it from no-intro's N64 collection.
Also play the original MM, the 3DS version changed a lot of things for worse. In the last thread some people mentioned how one of the most fun parts of the original MM was Zora Link's swimming mechanic. There are other frustrating changes like Twinmold being near invincible when it shouldn't (iirc).