A tachometer typically has 4 inputs - +12v, ground, signal and light.
+12v goes to switched power, you can tap into the power for the radio or cig lighter.
Ground goes to any good body ground.
Light get tapped into the power for your dash lights (or headlights, fog, light signal to the radio, etc.)
Signal typically goes to the negative side of the coil. I would think on a 96, you would still have standard distributor/coil setup, but if you have a coil pack, I am not sure how it would work. Possibly the cam or crank sensor.
You will need to run a wire through the firewall, be sure to use a grommet so the wire does not scrape against the hole.
You will need to mount the gauge to the vehicle some how. You could either screw it directly to the dash or the pillar. A generic pillar gauge pod would make it look a little better.