You have to install retroarch on your switch to play different emulation on your switch. After you installed retroarch you have to put some games on your SD card.
Start retroarch and search for your files, like GBA, N64 games pp.
Before you can run N64 games on retroarch you have to start any game on your switch while pressing and holding L and R on your console. After this a new menu will open. Now you are in full RAM mode and search retroarch. Start retroarch in full RAM mode. Choose your emulator, choose your game and have fun.