One may leave one's car here in a port, possibly with card left on display inside (7,3)
'one may leave one's car here' is the definition.
The answer is a location as well as being a singular noun. This is suggested by the definition.
'a port possibly with card left on display inside' is the wordplay.
I cannot quite see how this works, but
'a' is found in the answer.
'port' could be 'p' and 'p' is present in the answer.
'card' could be 'king' (king is a kind of card) and 'king' is found in the answer.
'left' could be 'l' (common abbreviation) and 'l' is found in the answer.
The remaining letters 'rot' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
'in' is the link.
Can you help me to learn more?
(Other definitions for parking lot that I've seen before include "Where cars are left in the US", "Place for autos in North America".)