To elaborate on what bigwillz is saying:
-Create an FX Channel (or Group Channel)
-Setup your delay plugin in one of the insert slots on this newly created channel (When creating an FX Channel, this will be done automatically).
-Now setup the delay to your setting of choice.
-Now on the channel(s) you want to use the delay, create a send to the appropriate FX Channel, activate the send and adjust the level.
-Now create a new automation lane for the track that you are working with, and select the respective send-slot/bypass function as the controller to edit.
This method is handy for creating a Delay that could be shared by many tracks.
If the delay is to be used on only one track, simply put it in an insert slot on the track you want effected, and create a new automation lane for that tracks insert-slot/bypass function.
If you are only be going to using an effect in certain spots, you can also create automation moves to bypass the actual effect processor (via its own track in project window). This can help preserve on CPU when the effect is not being used. But use the first method, to "Control" the effect, as using this second method could chop off delay/reverb tails etc.
Consult your manual for more info on setting up automation.
