Right,
This is how I do it:
Select range selection tool and highlight the section you want to add reverb to.
Go to Audio>Plug ins>reverb and select the reverb or any other plug in you want to use
At the bottom of the reverb ( or whatever effect you choose) GUI you will see some extra buttons or tabs which are:
More - Preview - Process - Cancel
By “preview”-ing you can hear the results of the parameters you’ve set for the particular section you have highlighted.
Once you are happy with the sound click “Process” at the bottom of the effect GUI
Job done,
Best,
Jim B