It has a special door (for Johnny?) (5)
I believe the answer is:
stage
'johnny?' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'it has a special door for' is the wordplay.
'it' becomes 'tag' (playground catching game).
'has' says to put letters next to each other.
'a special' becomes 'S' (common abbreviation as in Special Air Service).
'door for' becomes 'e' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'tag' after 's' is 'stag'.
'stag'+'e'='STAGE'
Can you help me to learn more?
(Other definitions for stage that I've seen before include "Mount (a play)" , "The boards" , "Platform for actors" , "Acting platform; coach" , "Leg, section" .)