Sets are arranged into part of mosaic (7)
I believe the answer is:
tessera
'part of mosaic' is the definition.
(I've seen this before)
'sets are arranged' is the wordplay.
'arranged' indicates an anagram (letters rearranged).
'sets'+'are'='setsare'
'setsare' anagrammed gives 'TESSERA'.
'into' acts as a link.
(Other definitions for tessera that I've seen before include "Piece of picture" , "Bit of design" , "Small stone for mosaics" , "Mosaic stone" , "Die" .)