[Rwp] interacting with plugins --ReaVerb for example?

[studio at kwaakproductions.com]

Hi y'all:
This might be a dated topic, but I have been progressing through the  
Reaper user guide, and I just hit a major roadblock. I'm experimenting  
with adding FX on a voice track. After selecting a plugin such as  
ReaVerb from the menu and then tabbing in the dialog, I come to a  
combo box with presets that I cannot navigate under any circumstances.  
Presing Shift+P to bring up the Plugin editor in ReaAccess does  
nothing. Will pressing the UI button allow me to navigate the combo  
boxes and unlabeled checkboxes, and what is the difference between the  
normal UI and the UI that displays after pressing the UI button?  
Thanks in advance for any assistance with this matter.