What one needs to be lithe and act fit (8)
I believe the answer is:
athletic
'what one needs to' is the definition.
I can't judge whether this defines the answer.
'lithe and act fit' is the wordplay.
'and' means one lot of letters go next to another (I've seen this in other clues).
'fit' is an anagram indicator (I've seen 'fits' mean this).
'lithe' put after 'act' is 'actlithe'.
'actlithe' is an anagram of 'ATHLETIC'.
'be' is the link.
Can you help me to learn more?
(Other definitions for athletic that I've seen before include "Lusty" , "Muscular" , "Good at running and jumping" , "Lithe cat (anag.)" , "Active, sporty" .)