To start an instant message or 'IM' with a pal...

select the 'pals tab' on the main 'pal list window'

scroll thru the list of online or offline pals

double click on their nickname with your left mouse button, or 'right click' on their nickname in the 'pal list' and select 'instant message pal' from the menu that appears

see instant message window

from within a chat room
'right click' on a name in the chat room participant list to select it

select 'instant message' from the menu that appears

see instant message window