Attractive periodical on net, nice centrefold (8)
I believe the answer is:
magnetic
'attractive' is the definition.
(synonyms)
'periodical on net nice centrefold' is the wordplay.
'periodical' becomes 'mag' (short for magazine).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'nice centrefold' becomes 'ic' (I can't explain this - if you can you should give a lot more credence to this answer).
'mag'+'net'+'ic'='MAGNETIC'
Can you help me to learn more?
(Other definitions for magnetic that I've seen before include "What's attractive" , "Having the property of attracting iron" , "Drawing" , "Attracting iron or steel" , "Able to attract metal, or charismatic" .)