Young lady to lie about cannon ball (7)
I believe the answer is:
missile
'cannon ball' is the definition.
'missile' can be an answer for 'ball' (thesaurus). I'm unsure of the 'cannon' bit.
'young lady to lie about' is the wordplay.
'young lady' becomes 'miss' (term of address for a young woman).
'to' means one lot of letters go next to another.
'about' indicates anagramming the letters.
'lie' with letters rearranged gives 'ile'.
'miss'+'ile'='MISSILE'
Can you help me to learn more?
(Other definitions for missile that I've seen before include "Military projectile" , "Cruise, perhaps" , "weapon that's fired" , "Object forcibly propelled at a target" , "Weapon that's thrown or projected" .)