Initially a call for help (3)
If this is the answer I cannot explain how the clue works.
Can you help me to learn more?
(Another definition for s o s that I've seen is " Distress call".)
'call for help' is the definition.
(SOS distress signal)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for sos that I've seen before include "Mayday call" , "Help code in 13 Across" , "plea" , "Morse Code for help" , "Coded distress signal" .)