See if your tv has yellow-video, red/white-audio inputs in the back. If so, just hook those same colored RCA cables into the N64's output holes, and choose the Video 1? input on the tv. Whatever it says under those input holes on the back of the tv is the input to choose from your remote to bring that input up on the tv. If you don't have a remote, look for a menu button on the front of the tv and start pressing it.
If all your tv has is a cable input, you'll need an rf modulator to use the N64.