Wherein to learn to play cards? (6)
I believe the answer is:
school
'play cards?' is the definition.
The definition and answer can be both related to time as well as being singular nouns.
Maybe there's a link between them I don't understand?
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for school that I've seen before include "Train - group of porpoises" , "Educational institution" , "Give instruction" , "eg Harrow" , "Group of sea creatures" .)