handhaben
to handle
To use, operate, or deal with a device, tool, or situation.
Er wusste nicht, wie man diese komplizierte Maschine handhaben muss.
He did not know how to handle this complicated machine.

to handle
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to handle
To use, operate, or deal with a device, tool, or situation.
Er wusste nicht, wie man diese komplizierte Maschine handhaben muss.
He did not know how to handle this complicated machine.

The verb 'handhaben' (to handle) can be derived from 'Hand' (hand) and 'haben' (to have). The literal idea is to have something 'in der Hand' (in one's hand) and therefore exercise control over it.
Diese Kamera ist sehr einfach zu handhaben.
This camera is very easy to handle.
'Handhaben' (to handle) is an inseparable verb. The stress is on the second syllable ('hand-HA-ben'), which is why the prefix 'hand-' always remains attached to the verb.
Er handhabt die schwierige Situation sehr professionell.
He handles the difficult situation very professionally.
You can recognize the meaning from the object: If it is a concrete object (tool, device), it means 'bedienen' (to operate). If it is something abstract (problem, rule, situation), it means 'damit umgehen' (to deal with it) or 'anwenden' (to apply).
Der neue Mitarbeiter kann die Software noch nicht gut handhaben.
The new employee cannot handle the software well yet.
In the meaning of 'bedienen' (to operate), 'handhaben' (to handle) is often used with objects such as 'ein Werkzeug' (a tool), 'eine Maschine' (a machine), 'ein Gerät' (a device), or 'eine Waffe' (a weapon).
Ein Chirurg muss seine Instrumente perfekt handhaben können.
A surgeon must be able to handle their instruments perfectly.
When dealing with rules or situations, 'handhaben' (to handle) is often combined with adverbs that describe the manner: to handle something 'flexibel' (flexibly), 'streng' (strictly), 'kulant' (accommodatingly), or 'vorsichtig' (carefully).
Die Universität handhabt die Anmeldungen sehr streng.
The university handles registrations very strictly.
to use
'verwenden' and 'handhaben' can both mean dealing with something in a practical way. 'verwenden' emphasizes the purpose: you use something in order to achieve a goal. 'handhaben' emphasizes more the way you operate, control, or deal with a situation. With a device, both can fit, but with a difference: you use a device for a task, and you handle it safely or correctly. 'handhaben' also fits with rules or procedures when the point is how they are applied. Learners may confuse the words because both have to do with use, but 'handhaben' focuses more on the how.

Der neue Mitarbeiter hat gelernt, wie man die Maschine sicher handhabt.
The new employee has learned how to handle the machine safely.
Nach dem Essen verwendet sie eine App, um ihre Medikamente nicht zu vergessen.
After eating, she uses an app so she does not forget her medication.