Have fun on a beach (5)
I believe the answer is:
playa
'beach' is the definition.
(I have seen 'Spanish beach ' mean 'playa' so perhaps 'beach' could also mean 'playa')
'have fun on a' is the wordplay.
'have fun' becomes 'play' (I've seen this in another clue).
'on' says to put letters next to each other.
'play'+'a'='PLAYA'
(Other definitions for playa that I've seen before include "lake after rainfall" , "Spanish beach" , "piece of land liable to flood" , "bed in Spain" , "Expanse of dry land" .)