
einstellen
to hire
To give someone a job; to employ someone.
Die Firma stellt ab nächstem Monat fünf neue Ingenieure ein.
The company is hiring five new engineers starting next month.
to hire / adjust / stop
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to hire
To give someone a job; to employ someone.
Die Firma stellt ab nächstem Monat fünf neue Ingenieure ein.
The company is hiring five new engineers starting next month.

to adjust / set
To adjust or regulate a device, machine, or system in order to achieve a desired function or state.
Kannst du bitte den Radiosender auf 98.5 einstellen?
Can you please set the radio station to 98.5?

to stop / discontinue
To end or give up an activity, production, or service.
Die Bahn hat den Betrieb auf dieser Strecke letztes Jahr eingestellt.
The railway discontinued service on this route last year.

to prepare for
To prepare oneself mentally or practically for a future situation or event.
Die Wanderer müssen sich auf einen plötzlichen Wetterumschwung einstellen.
The hikers have to prepare for a sudden change in the weather.

to set in
The occurrence or beginning of a state, feeling, or symptom.
Nach der Einnahme des Medikaments stellte sich schnell eine Besserung ein.
After taking the medication, an improvement quickly set in.

to put away / store
To put something in a protected place, for example for storage or overwintering.
Im Winter stellen wir die Gartenmöbel in der Garage ein.
In winter, we store the garden furniture in the garage.
'Einstellen' is a separable verb with the prefix 'ein-'. In a main clause in the present or simple past tense, the prefix goes to the end of the sentence. In subordinate clauses and in the infinitive, the verb stays together.
Er stellt den Fernseher leiser ein.
He turns the TV down.
Since 'einstellen' has many meanings, context is crucial. If it is about people, it means 'anstellen' (to hire). With devices, it means 'justieren' (to adjust). With activities, it means 'beenden' (to stop/end). The reflexive form 'sich einstellen' has other meanings again.
Die Firma stellt neue Mitarbeiter ein.
The company is hiring new employees.
In the meaning 'to prepare oneself', the verb is always used reflexively and with the preposition 'auf' plus accusative: 'sich auf etwas einstellen' (to prepare for something).
Wir müssen uns auf schlechtes Wetter einstellen.
We have to prepare for bad weather.
When 'sich einstellen' is used without a preposition, it means that a state or feeling begins by itself. The subject is often something abstract, such as 'Erfolg' (success), 'Ruhe' (calm), or 'ein Gefühl' (a feeling).
Nach einer Weile stellte sich ein Gefühl der Zufriedenheit ein.
After a while, a feeling of satisfaction set in.
In the meaning of 'employing someone', typical objects are 'Mitarbeiter' (employees), 'Personal' (staff), or 'Auszubildende' (trainees/apprentices). You can also say that someone is hired 'fest' (permanently) or 'befristet' (for a fixed term).
Das Unternehmen stellt zum neuen Jahr 20 Auszubildende ein.
The company is hiring 20 trainees at the start of the new year.
When it comes to adjusting devices, 'einstellen' is often combined with 'Heizung' (heating), 'Radio' (radio), 'Wecker' (alarm clock), 'Temperatur' (temperature), or 'Lautstärke' (volume).
Ich habe vergessen, den Wecker für morgen früh einzustellen.
I forgot to set the alarm clock for tomorrow morning.
The meaning 'to stop/end' is often used in formal or official contexts. Typical objects are 'der Betrieb' (operations/service), 'die Produktion' (production), 'die Zahlungen' (payments), or 'die Ermittlungen' (investigations).
Die Polizei hat die Ermittlungen aus Mangel an Beweisen eingestellt.
The police discontinued the investigation due to a lack of evidence.
to record / take in
Einstellen means giving someone a job. Aufnehmen, on the other hand, emphasizes that the person becomes part of a group or organization. Einstellen fits when an employment relationship begins; aufnehmen is more appropriate when someone is integrated into a team.

Die Firma stellt Lara als Entwicklerin ein.
The company hires Lara as a developer.
Nach ihrer Einstellung nimmt die Firma Lara in das Entwicklungsteam auf.
After hiring Lara, the company brings her into the development team.