A brief engagement is good for Joe (3)
I believe the answer is:
gig
'a brief engagement' is the definition.
'gig' can be an answer for 'engagement' (gig is a kind of engagement). I am not certain of the 'a brief' bit.
'good for joe' is the wordplay.
'good' becomes 'g' (abbreviation).
'for' means one lot of letters go next to another (I've seen this in other clues).
'joe' becomes 'gi' (GI Joe).
'g' put after 'gi' is 'GIG'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for gig that I've seen before include "Live performance by musicians" , "Live musical performance" , "A single musical performance - it's a palindrome" , "A one-night entertainment" , "Small horse-drawn carriage" .)