if the alarm has a button for it, it'll be easy to install. Chances are it is a transistor output on the alarm, so it will need a relay. The output on the alarm will trigger the relay to send power to the solenoid.

You'll need to figure out which wire on the alarm is for that purpose, and also what polarity (+ or-) it is.

The downfall to those kits (usually made by autoloc) is, it sounds like someone hit your trunk with a sledge hammer when you pop it, they're pretty damn loud.

If you're really confused about it, i'd suggest going back to the place that installed it and see what they'd charge to do it.