Computer used by person in American diner (6)
I believe the answer is:
server
'computer' is the definition.
'used by person in american diner' is the wordplay.
'used by' indicates putting letters inside.
'person' becomes 'seer' (seer is a kind of person).
'in american diner' becomes 'rv' (I can't justify this - if you can you should believe this answer much more).
'seer' enclosing 'rv' is 'SERVER'.
Can you help me to learn more?
(Other definitions for server that I've seen before include "Priest's assistant" , "The one who sets the ball in play at tennis" , "Waiter, waitress" , "Meal attendant" , "Computer network access managing device" .)