Fashion line for one on catwalk (5)
'fashion' is the definition.
(I've seen this before)
'line for one on catwalk' is the wordplay.
'line' becomes 'el' (el is a kind of line).
'for' is a charade indicator (letters next to each other) (I've seen this in other clues).
'one on catwalk' becomes 'mod' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'el' put after 'mod' is 'MODEL'.
Can you help me to learn more?
(Other definitions for model that I've seen before include "Moss, say", "(Person functioning as) example", "Clothes displayer", "Example (on the catwalk?)", "Small-scale version".)