The people from northern Europe said these are used for swimming (5)
I believe the answer is:
finns
'the' is the definition.
I can't judge whether this definition defines the answer.
'people from northern europe said these are used for swimming' is the wordplay.
I cannot quite see how this works, but
'from' could be 'in' (I've seen this in other clues) and 'in' is found in the answer.
'northern' could be 'n' (abbreviation e.g. N. Ireland) and 'n' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for finns that I've seen before include "Natives of Helsinki" , "foreigners" .)