im using the Twisted Lemon Sidekick v3 as the compressor. you can find it at twistedlemon.nl
(dont worry its free )
First, start by making a new project, and create a track for your kick.
then create another track, rename it "SC buss" or whatever you like, and drop the sidekick plugin onto it.
The plugins initial state is bypassed so dont forget to turn that switch off (the source of many wtf is going wrong moments for me)
turn on the use "virtual channel a" button, and set it to "ducking" mode

on the SC buss channel (or whatever you called it) set it to monitor "in" and set it to recieve audio from the kick channel

now make a new channel and drop whatever you like onto it. this channel is the audio that will be ducking in time with the kick. its probably best for the purposes of this tutorial to grab a synth and find a nice long, sustained pad sound.
next, change the pad channels audio path from "master" to "SC buss", and now the compressor should be receiving audio from the synth.

if all has gone well you should see information through both channels and the compressor when you trigger the synth

now stick a whole bunch of kicks in the first channel to give the pad something to duck under, play your pad sound, and away you go!