Re: A question about gate in Logic...
To make a gated synth like the pre-sets have in the "Gated Synths" section of the library, I think you would need a few things to build it from the bottom up. First, a pad with a good amount of sustain or reverb. Second, a noise gate plug-in. Third, a silent track with a kick or snare drum that can trigger the noise gate, bussed to an Aux track.
Place the noise gate on the Pad channel strip, and side chain it to the Aux track that your Kick or Snare is being sent to. Make sure the Original channel strip where your drum is located is set to "no output." Now set the level of the kick drum to a point where it will activate the noise gate and give you that effect! You may have to tweak the controls a bit to get the specific amount of gate to your liking. Once that's done you can then apply the appropriate EQ, reverb, delay...whatever other plug-in you think is necessary for the effect you desire.
The same sort of gating effect could also be achieved by using an LFO in the synth you choose to produce the pad sound, but it doesn't quite have the same type of sound as gating makes.
You could also simply use the "Space designer" plug-in to create neat gating effects, but that plug in is a bit high on the learning curve compared to other plug-ins Logic has. Try it!
Hope this helps.