als, wenn or wann: German's three ways of saying «when»

German has three words where your language has one. wann is for ASKING, directly or indirectly. als is for ONE time in the past: Als ich klein war. wenn is for everything else — repeated events, plus the present and the future. All three send the verb to the end except wann in a direct question.

The usual slip. Using wenn for a one-off past event, the commonest case when telling a story. «When I got to Berlin» is Als ich nach Berlin kam. wenn in the past means «whenever», so the sentence changes meaning without warning. The second mistake is using wann outside a question.

Why it catches you out. English uses «when» for all three too, and «whenever» for the repeated one, which is exactly wenn. So half the distinction is already there: whenever = wenn, question word = wann. What English has no word for is als, the single past event, and that is the one to build.