besetzen
to occupy
To claim or take a place, seat, or room for oneself so that it is no longer available to others.
Entschuldigung, ist dieser Stuhl noch besetzt?
Excuse me, is this chair still occupied?

to occupy / fill / cast
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to occupy
To claim or take a place, seat, or room for oneself so that it is no longer available to others.
Entschuldigung, ist dieser Stuhl noch besetzt?
Excuse me, is this chair still occupied?

'Besetzen' (to occupy / fill / cast) is an inseparable verb. The prefix 'be-' remains firmly attached to the stem verb 'setzen' (to set / put) in all tenses and sentence constructions.
Er besetzt seit einer Stunde den besten Platz am Fenster.
He has been occupying the best seat by the window for an hour.
The exact meaning of 'besetzen' (to occupy / fill / cast) is almost always made clear by the object of the sentence. Pay attention to whether the sentence is talking about a place, a job, a role in a film, or a territory.
Die Demonstranten besetzten den zentralen Platz der Stadt.
The demonstrators occupied the city's central square.
The past participle 'besetzt' (occupied / taken) is very often used like an adjective to describe that a seat, a phone line, or a toilet is not free.
Ich konnte dich nicht anrufen, die Leitung war ständig besetzt.
I couldn't call you; the line was constantly busy.
In a professional context, 'besetzen' (to fill) is often combined with words such as 'Stelle' (position), 'Position' (position), or 'Amt' (office). The passive is also often used here.
Die Firma konnte die offene Position schnell neu besetzen.
The company was able to fill the open position quickly.
When it is about casting a role, the person is often introduced with the preposition 'mit' and the dative. The structure is: 'eine Rolle mit jemandem besetzen' (to cast a role with someone).
Man hat die Nebenrolle mit einem Nachwuchstalent besetzt.
The supporting role was cast with a young up-and-coming talent.
to hire / adjust / stop
'einstellen' and 'besetzen' can both have to do with a job or role. 'einstellen' means that someone gets a job and works for a company. It is about the person and the employment relationship. 'besetzen' means that an open position, job, or role is filled with a person. It emphasizes the position or role itself more. In theater or film, you also say that a role is 'besetzt' (cast). Learners may confuse the words because both occur in job contexts. In everyday language, you say: a company 'stellt eine Person ein' (hires a person), but it 'besetzt eine Stelle' (fills a position).

Ab März ist die freie Stelle im Büro wieder besetzt.
Starting in March, the open position in the office will be filled again.
Nach dem Gespräch stellt die Bäckerei einen neuen Verkäufer ein.
After the interview, the bakery hires a new salesperson.