aufbrechen
to set off
To start on one's way; to begin a trip, hike, or march.
Wir müssen früh aufbrechen, wenn wir vor Einbruch der Dunkelheit ankommen wollen.
We have to set off early if we want to arrive before nightfall.

to set off / to break open
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to set off
To start on one's way; to begin a trip, hike, or march.
Wir müssen früh aufbrechen, wenn wir vor Einbruch der Dunkelheit ankommen wollen.
We have to set off early if we want to arrive before nightfall.

'Aufbrechen' is a separable verb. The prefix 'auf-' stands at the end in a main clause. In subordinate clauses and in the infinitive with 'zu', the verb stays together.
Wir brechen morgen bei Sonnenaufgang auf.
We are setting off tomorrow at sunrise.
The perfect tense is formed with 'sein' (to be) when it is about movement (starting a journey) or a change of state (a bud opens). For an active action with an object (opening a door), 'haben' (to have) is used.
Die Wandergruppe ist schon aufgebrochen.
The hiking group has already set off.
When 'aufbrechen' is used without an object, it usually means 'sich auf den Weg machen' (to set off). If it has an object, it often means 'gewaltsam öffnen' (to break open by force) with concrete objects, or 'verändern' (to change) with abstract terms.
Die Bergsteiger brechen in einer Stunde auf.
The mountaineers are setting off in an hour.
In a figurative, abstract meaning, 'aufbrechen' is often used with nouns such as 'Strukturen' (structures), 'Regeln' (rules), 'Denkmuster' (patterns of thought), or 'Traditionen' (traditions) to describe modernization or dissolution.
Die neue Chefin will die starren Hierarchien im Unternehmen aufbrechen.
The new boss wants to break up the rigid hierarchies in the company.
to go
'gehen' and 'aufbrechen' can both mean that you leave a place and move toward a destination. 'gehen' is very general and fits many everyday situations: you go home, to work, or out of the room. 'aufbrechen' sounds more purposeful and emphasizes the beginning of a route, a trip, or a longer undertaking. It is often used when several people set off by vehicle or on foot and there is a plan behind it. In everyday language, 'gehen' is usually more neutral, while 'aufbrechen' is a bit more deliberate and often more formal, solemn, or organized.

Am frühen Morgen brechen wir zu unserer Wanderung auf.
Early in the morning, we set off on our hike.
Clara geht nach dem Gespräch zur Bushaltestelle.
After the conversation, Clara goes to the bus stop.