Route wire through or around camera helmet so that only the switch and a small length of wire is exposed.
Set your camera to the desired operating mode.
Trigger the shutter release by pushing your tongue forward against the switch face (the dot). You should feel a "click" as you actuate the switch. A brief push will take a single exposure, a longer push takes multiple exposures.
Turn off your camera and and disconnect switch between uses.
When you first get your switch, practice on the ground with no film. You should feel a subtle "click" as you actuate the switch. Even though you might not feel it as well in freefall, you'll quickly gain the confidence to know when you have taken an exposure. Trust your tongue.
Take a test shot before each dive to verify proper functioning
Place the switch firmly against your front teeth before tightening your helmet. This positions the switch for optimum ease of use.
Try using manual focus with the focus ring set at the expected distance of your subject. You'll save batteries and get shots more quickly since your camera won't need to focus constantly.
Don't expose your switch to very hot or cold environments.
Turn off your camera between dives and unplug switch while not in use. Not doing this may shorten battery life.
The single/multiple exposure capabilities are dependent upon your camera. Most will take a single shot with a short push and between 5-11 shots per second if you push and hold. Be sure to set your camera to "continuous" or equivalent setting for desired results.