Discovered seaside town's fine (6)
I believe the answer is:
righto
'fine' is the definition.
(both can mean 'yes' or 'alright')
'discovered seaside town's' is the wordplay.
'discovered' indicates the central letters (dis-covered - outer letters removed).
'seaside town' becomes 'Brighton' (Brighton is by the sea).
The central letters of 'brighton' are 'RIGHTO'.
(Other definitions for righto that I've seen before include "fine" , "I agree (informal)" , "very well" , "Okey-dokey" , "OK" .)