Consult the repair manual for your specific vehicle, and make adjustments accordingly.
Warm up the engine, and then turn it off.
To disconnect the engine control unit, disconnect the wire from terminal 15, or unplug the coil packs to disable the ignition system.
Remove one spark plug. Read the tester kit's instructions to determine which adapter to use. Install the adapter in place of the spark plug.
Attach the fitting on the rubber hose to the adapter. Twist the hose by hand to screw it into place.
Pull back the metal collar on the dial gauge, and insert the opposite end of the hose into the gauge's fitting. Slide the collar over the hose's fitting.
Insert the key into the ignition. Turn the key, and hold it for 10 seconds. Write down the reading.
Press the button on the side of the gauge's fitting to release the compressed air.
Uninstall the tester kit, and reinstall the spark plug.
Repeat the test with the remaining cylinders. Consult your repair manual to determine where the readings stand for your vehicle.