Took cornet out of trench coat or that's the talk online (4)
I believe the answer is:
chat
'that's the talk online' is the definition.
(I've seen this in another clue)
'took cornet out of trench coat' is the wordplay.
'took' becomes 'cat' (I can't justify this - if you can you should believe this answer much more).
'out' indicates named letters should be taken away.
'of' becomes 'o''.
'coat' indicates putting letters inside.
'o'+'trench'='otrench'
'otrench' with 'cornet' taken out is 'h'.
'cat' placed around 'h' is 'CHAT'.
'or' is the link.
Can you help me to learn more?
(Other definitions for chat that I've seen before include "waffle?" , "Natter" , "Tom in 22 [ALSACE]" , "Exchange text or voice messages through a computer" , "Talk familiarly" .)