Link it up with an ear-piece (3)
I believe the answer is:
tie
'link' is the definition.
(I know that link can be written as tie)
'it up with an ear-piece' is the wordplay.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'with' says to put letters next to each other.
'an ear-piece' becomes 'e' (this could be a standard abbreviation I've not previously seen).
'it' reversed gives 'ti'.
'ti'+'e'='TIE'
Can you help me to learn more?
(Other definitions for tie that I've seen before include "Encumbrance" , "Bond; neckwear" , "Equal score" , "Join, link" , "Fasten the neckwear" .)