Along with the letter, poem put in secret text (6)
I believe the answer is:
encode
'put in secret text' is the definition.
The answer and definition can be both to do with communicating as well as being verbs in their base form.
Perhaps they are linked in a way I don't understand?
'along with the letter poem' is the wordplay.
'along with' says to put letters next to each other.
'the letter' becomes 'enc' (I can't justify this - if you can you should believe this answer much more).
'poem' becomes 'ode' (ode is a kind of poem).
'enc' next to 'ode' is 'ENCODE'.
Can you help me to learn more?
(Other definitions for encode that I've seen before include "Put into cypher" , "Put (message) into ciphers" , "transform with substitutions?" , "Make cryptic" , "Put into secret symbols" .)