Stamp a letter, we understand (5)
I believe the answer is:
tread
'stamp a letter' is the definition.
'tread' can be an answer for 'stamp' (I've seen this in another clue). I'm unsure of the 'a letter' bit.
'we understand' is the wordplay.
'we' becomes 't' (I can't explain this - if you can you should believe this answer much more).
'understand' becomes 'read' (read can mean to understand or analyse).
't'+'read'='TREAD'
Can you help me to learn more?
(Other definitions for tread that I've seen before include "between the car and the road" , "Moulded part of a tyre" , "Stomp heavily" , "way of dancing" , "Surface of car tyre" .)