The most common and most likely answer to this crossword clue is the 10 letter word EXPOUNDING
I've seen this crossword clue in The Guardian
E
X
P
O
U
N
D
I
N
G
Buddy explains!
The straight part
We know that "Setting out" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case setting out = expounding.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does EXPOUNDING mean?
EXPOUNDING verb- To set out the meaning of; to explain or discuss at length
- To make a statement, especially at length.
- The act by which something is expounded.