One sets off, going from the outside into German city (7)
I believe the answer is:
trigger
'one sets off going from' is the definition.
I can't judge whether this definition defines the answer.
'outside into german city' is the wordplay.
'outside' becomes 'gg' (I can't explain this - if you can you should give a lot more credence to this answer).
'into' is an insertion indicator.
'german city' becomes 'trier' (Trier is a city in Germany).
'gg' placed within 'trier' is 'TRIGGER'.
'the' is the link.
Can you help me to learn more?
(Other definitions for trigger that I've seen before include "Releasing device" , "Set in motion - say gunfire" , "Component of gun" , "Start" , "arm with this?" .)