wann
when
Used as a question word to ask about the point in time or duration of something.
Wann kommt der nächste Bus nach Berlin?
When does the next bus to Berlin arrive?

when
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when
Used as a question word to ask about the point in time or duration of something.
Wann kommt der nächste Bus nach Berlin?
When does the next bus to Berlin arrive?

The position of the verb changes depending on the function of 'wann' (when). In a direct question, the conjugated verb is in position 2. If 'wann' introduces a subordinate clause, the conjugated verb comes at the end of the clause.
Wann fängt der Film an?
When does the film start?
'Wann' (when) is often used in typical everyday questions to ask about start and end points or schedules. Examples include 'Wann beginnt...?' (When does ... begin?), 'Wann hat ... geöffnet?' (When is ... open?), or 'Wann fährt ... ab?' (When does ... depart?).
Wann hat der Supermarkt geöffnet?
When is the supermarket open?
The expression 'dann und wann' means 'sometimes' or 'occasionally'. It is often used to describe an irregular but recurring action.
Wir gehen nur dann und wann ins Kino.
We only go to the movies now and then.
if / when
'wenn' and 'wann' are both often connected with time, but they are used differently. 'wenn' introduces a subordinate clause and describes a condition or a point in time: something happens if/when something else happens. 'wann' asks about a time or appears in an indirect question. Learners can easily confuse the words because both occur in sentences about time. A simple tip is: when asking about the time, use 'wann'. For a condition or a time in a subordinate clause, you usually use 'wenn'.

Frau Schneider fragt in der E-Mail, wann die Besprechung beginnt.
In the email, Ms. Schneider asks when the meeting starts.
Wenn ich heute früher fertig bin, gehe ich noch zum Training.
If I finish earlier today, I'll still go to training.