die Handhabung
handling
The way in which you operate or use a device, tool, or vehicle.
Die Handhabung der neuen Kaffeemaschine ist sehr einfach.
The handling of the new coffee machine is very easy.

handling
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handling
The way in which you operate or use a device, tool, or vehicle.
Die Handhabung der neuen Kaffeemaschine ist sehr einfach.
The handling of the new coffee machine is very easy.

'Handhabung' (handling) is the noun form of the verb 'handhaben' (to handle). This verb is made up of 'Hand' (hand) and 'haben' (to have) and literally means to have something 'in der Hand' (in your hand), meaning to have control over it.
Er muss den richtigen Umgang mit der Verantwortung erst lernen.
He first has to learn the right way to deal with responsibility.
The meaning depends on what the word refers to. The 'Handhabung' (handling) of a device or tool is its operation. The 'Handhabung' (handling) of a problem or situation is the administrative or strategic way of dealing with it.
Die Handhabung dieser Software ist nicht sehr intuitiv.
The handling of this software is not very intuitive.
Common adjectives combined with 'Handhabung' (handling) are 'einfach' (simple), 'kompliziert' (complicated), 'sicher' (safe), or 'korrekt' (correct). These describe how well or poorly something is operated or managed.
Eine einfache Handhabung war uns beim Kauf des Geräts wichtig.
Easy handling was important to us when buying the device.
treatment
'die Behandlung' and 'die Handhabung' can both describe how one deals with something. 'Behandlung' is broader and can refer to people, animals, things, or also the way something is handled. 'Handhabung' is especially suitable for devices, tools, vehicles, or a procedure. It is about how something is used, operated, or carried out in practice. The words can be confused because both have to do with 'Umgang' (dealing with / handling). With people, you normally use 'Behandlung', not 'Handhabung'. With devices and practical processes, 'Handhabung' sounds more precise.

Vor der Reise erklärt mir Tom die Handhabung der neuen Kamera.
Before the trip, Tom explains to me how to handle the new camera.
Die freundliche Behandlung der Kundin hat im Geschäft einen guten Eindruck gemacht.
The friendly treatment of the customer made a good impression in the store.