Spend money to secure Lessing's first dramatic work (4)
'dramatic work' is the definition.
(play is a kind of dramatic work)
'spend money to secure lessing's first' is the wordplay.
'spend money' becomes 'pay' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'to secure' means one lot of letters goes inside another.
'lessing's first' becomes 'l' (pst letter of 'lessing').
'pay' placed around 'l' is 'PLAY'.
Can you help me to learn more?
(Other definitions for play that I've seen before include "Work for actors", "Stage drama", "Participate in games or sport", "Have fun -- theatrical work", "Portray in a drama".)