All set to decode unknown (5)
I believe the answer is:
ready
'all set' is the definition.
(I've seen this before)
'decode unknown' is the wordplay.
I cannot really see how this works, but
'unknown' could be 'y' (algebra) and 'y' is found within the answer.
The remaining letters 'read' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'to' is the link.
Can you help me to learn more?
(Other definitions for ready that I've seen before include "Fully-prepared" , "In addition" , "Prepare < dough" , "Cash; within reach" , "game?" .)