austreten
to leave
To officially end membership in an organization, association, party, or religious community.
Sie hat beschlossen, aus der Kirche auszutreten.
She decided to leave the church.

to leave / to leak / to stamp out
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to leave
To officially end membership in an organization, association, party, or religious community.
Sie hat beschlossen, aus der Kirche auszutreten.
She decided to leave the church.

'Austreten' (to leave/leak/stamp out) is a separable verb. The prefix 'aus-' stands at the end of the sentence in main clauses. In subordinate clauses and in the infinitive, the verb stays together.
Er tritt morgen aus dem Verein aus.
He is leaving the club tomorrow.
The perfect tense of 'austreten' is almost always formed with the auxiliary verb 'sein', because it describes a change of state or movement. For example: 'Das Wasser ist ausgetreten.' (The water has leaked out/overflowed.)
Nach dem starken Regen ist der Bach ausgetreten.
After the heavy rain, the stream overflowed.
When ending a membership, you use the structure 'aus etwas (Dativ) austreten' (to leave something, with the dative after aus). Typical organizations are 'die Kirche' (the church), 'ein Verein' (an association/club), or 'eine Partei' (a party).
Mein Bruder ist letztes Jahr aus dem Fußballverein ausgetreten.
My brother left the football club last year.
When the subject of the sentence is a liquid (oil, water) or a gas, 'austreten' means 'entweichen' (to escape) or 'auslaufen' (to leak out). The subject here is always impersonal.
Achtung, aus dem Fass tritt eine unbekannte Flüssigkeit aus.
Careful, an unknown liquid is leaking from the barrel.
In the meaning 'zur Toilette gehen' (to go to the toilet), 'austreten' is a euphemism, meaning a nicer indirect expression. It sounds somewhat more polite and formal, but it is rather rare in everyday use.
Kann ich kurz austreten, bevor der Film anfängt?
Can I step out briefly before the film starts?
Only in the meaning 'etwas mit den Füßen löschen' (to put something out with one's feet) is 'austreten' transitive and requires an accusative object. You stamp *something* out.
Er hat das kleine Lagerfeuer mit seinen Stiefeln ausgetreten.
He stamped out the small campfire with his boots.
to extinguish / delete
'löschen' and 'austreten' can both mean that something stops burning. 'löschen' is the general word: you can 'löschen' a fire with water, sand, or a fire extinguisher. 'austreten' only fits when you put out something burning with your foot, for example a cigarette or a small ember. For a large fire, you do not say 'austreten', but 'löschen'.

Anton tritt die glühende Zigarette vor der Tür aus.
Anton stamps out the glowing cigarette in front of the door.
Die Feuerwehr löscht den Brand mit viel Wasser.
The fire department is extinguishing the fire with a lot of water.