One past event or repeated occasions?
Als ich ankam, regnete es.
Distinguish a single past situation from repeated or conditional situations.
Use als for a single past event or a bounded past period: Als ich ein Kind war, wohnte ich am Meer. It need not mean one brief moment. Use wenn for repeated occasions, present/future time or a condition. Immer wenn makes repetition explicit. Both introduce subordinate clauses with the finite verb at the end. When the subordinate clause comes first, the following main clause begins with its finite verb: Als ich ankam, regnete es. Choose from the intended meaning, not simply because a sentence contains a past tense.
Als ich ankam, regnete es.
When I arrived, it was raining.
Als ich ein Kind war, wohnte ich am Meer.
When I was a child, I lived by the sea.
Immer wenn wir Ferien hatten, besuchten wir Oma.
Whenever we had holidays, we visited Grandma.
Wenn ich morgen Zeit habe, rufe ich dich an.
If I have time tomorrow, I will call you.
Als der Kurs begann, war ich schon da.
When the course began, I was already there.
Wenn etwas unklar war, fragte ich nach.
Whenever something was unclear, I asked.
Use als for a single past event or a bounded past period: Als ich ein Kind war, wohnte ich am Meer. It need not mean one brief moment. Use wenn for repeated occasions, present/future time or a condition. Immer wenn makes repetition explicit. Both introduce subordinate clauses with the finite verb at the end. When the subordinate clause comes first, the following main clause begins with its finite verb: Als ich ankam, regnete es. Choose from the intended meaning, not simply because a sentence contains a past tense.
Distinguish a single past situation from repeated or conditional situations.
Wenn ich gestern zum ersten Mal ankam is unsuitable for the explicitly single past arrival here; use als. Not every past sentence takes als.
Single past event/period: als. Repetition or condition: wenn. Subordinate finite verb last; following main verb first.
Write four sentences: one first arrival, one period in childhood, one repeated past habit and one future condition. Explain why you selected als or wenn.