Make an application, or joke about it, possibly (3,2)
I believe the answer is:
put in
'make an application' is the definition.
'put in' can be an answer for 'make' (thesaurus). I'm unsure of the 'an application' bit.
'joke about it possibly' is the wordplay.
'joke' becomes 'pun' (punning is a kind of joking).
'about' indicates putting letters inside.
'possibly' indicates anagramming the letters.
'it' anagrammed gives 'ti'.
'pun' enclosing 'ti' is 'PUT-IN'.
'or' is the link.
Can you help me to learn more?
(Other definitions for put in that I've seen before include "Rugby throw to a set scrum" , "being asked to bat" , "Insert" , "Russian president" , "Submit" .)