herstellen
to produce
To create or make a product through a work process, usually industrially or by craft.
Diese Fabrik stellt Autoteile für verschiedene Marken her.
This factory produces car parts for various brands.

to produce / establish
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to produce
To create or make a product through a work process, usually industrially or by craft.
Diese Fabrik stellt Autoteile für verschiedene Marken her.
This factory produces car parts for various brands.

'Herstellen' (to produce / establish) is a separable verb. The prefix 'her' comes at the end in a main clause, stays attached to the verb in subordinate clauses, and in the infinitive with 'zu', 'zu' comes in between.
Die Firma stellt seit 20 Jahren Möbel her.
The company has been producing furniture for 20 years.
The word consists of the prefix 'her' (to here) and the verb 'stellen' (to put/place). Literally, it means to put something in a place so that it is available. From this developed the meaning 'produzieren' (to produce) or 'erschaffen' (to create).
In diesem Werk werden hochwertige Uhren hergestellt.
High-quality watches are produced in this plant.
The context reveals the meaning. If it is about a physical product like a car or a medication, 'herstellen' means 'produzieren' (to produce). If it is about something abstract like a connection or contact, it means 'schaffen' (to create) or 'aufbauen' (to build up/establish).
Dieses Unternehmen stellt umweltfreundliche Verpackungen her.
This company produces environmentally friendly packaging.
to do / make
'machen' and 'herstellen' can both mean that something is created. 'machen' is very general and fits in many everyday situations, for example when cooking, crafting, or preparing something. 'herstellen' sounds more precise and often more factual. It is used especially when products are created through work, technology, or craft. You can also 'herstellen' a connection or contact. If you simply want to say that someone is making something, 'machen' is often enough. If the production process is important, 'herstellen' fits better.

Die kleine Firma stellt Möbel aus altem Holz her.
The small company produces furniture from old wood.
Nele macht am Sonntag einen Kuchen für ihre Nachbarn.
On Sunday, Nele is making a cake for her neighbors.