The most common and most likely answer to this crossword clue is the 9 letter word DECALOGUE
I've seen this crossword clue in The Times
D
E
C
A
L
O
G
U
E
Buddy explains!
The straight part
We know that "set of instructions" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case set of instructions = decalogue.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 DECALOGUE mean?
DECALOGUE noun- Any set of rules that have the weight of authority