anstehen
to queue
To wait in a line or queue in order to get one's turn.
Wir mussten eine halbe Stunde an der Kasse anstehen.
We had to queue at the checkout for half an hour.

to queue / be coming up
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to queue
To wait in a line or queue in order to get one's turn.
Wir mussten eine halbe Stunde an der Kasse anstehen.
We had to queue at the checkout for half an hour.

'Anstehen' (to queue / be coming up) is a separable verb. The prefix 'an' comes at the end in main clauses; in subordinate clauses the verb stays together, and in the infinitive with 'zu', 'zu' stands between 'an' and 'stehen'.
Welche Aufgaben stehen heute an?
Which tasks are coming up today?
You can recognize the meaning from the subject: if a person 'ansteht' (queues), they are waiting in a line. If a thing or event (e.g., 'Prüfung' (exam), 'Fest' (celebration)) 'ansteht' (is coming up), it is planned as the next thing.
Viele Leute stehen für die neuen Konzertkarten an.
Many people are queuing for the new concert tickets.
When you are waiting in a line, 'anstehen' (to queue) is often combined with an indication of place that begins with 'an' or 'vor'. Typical phrases are 'an der Kasse anstehen' (to queue at the checkout), 'am Schalter anstehen' (to queue at the counter), or 'vor dem Kino anstehen' (to queue in front of the cinema).
Ich musste zwanzig Minuten am Postschalter anstehen.
I had to queue at the post office counter for twenty minutes.
In the meaning 'bevorstehen' (to be imminent), the verb is often used with abstract nouns for events or tasks. Common combinations are 'eine Prüfung steht an' (an exam is coming up), 'eine Entscheidung steht an' (a decision is coming up), or 'eine Reise steht an' (a trip is coming up).
Bald steht die wichtige Konferenz mit unseren Partnern an.
The important conference with our partners is coming up soon.
In the meaning 'zögern' (to hesitate), 'anstehen' is almost always negated and used with an infinitive construction: 'nicht anstehen, etwas zu tun' (not to hesitate to do something).
Der Chef stand nicht an, den Fehler direkt anzusprechen.
The boss did not hesitate to address the mistake directly.
The meaning 'jemandem gut stehen' (to suit someone well, referring to clothing) is very rare today and sounds old-fashioned. It is found mainly in older literature.
In dem alten Roman stand der Heldin ihr Ballkleid wunderbar an.
In the old novel, the heroine's ball gown suited her wonderfully.
to stand
'stehen' and 'anstehen' can both mean that a person is on their feet and not sitting. The important difference is the reason: 'stehen' only describes the posture or the location. 'anstehen' is used when you are waiting in a line, for example at the checkout or in front of a counter. Learners may confuse the words because when you are 'anstehen', you are usually standing. But not every instance of standing is 'anstehen'. Remember: someone who is 'ansteht' is waiting for their turn.

Vor der Bäckerei stehen am Morgen viele Kunden an.
In the morning, many customers queue in front of the bakery.
Im Bus steht Anna neben der Tür, weil kein Platz mehr frei ist.
On the bus, Anna is standing next to the door because there are no seats left.