das Geschäft
shop
A store or business premises where goods are sold or services are offered.
Ich muss noch schnell ins Geschäft, um Milch zu kaufen.
I still have to quickly go to the shop to buy milk.

shop / business
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shop
A store or business premises where goods are sold or services are offered.
Ich muss noch schnell ins Geschäft, um Milch zu kaufen.
I still have to quickly go to the shop to buy milk.

The word 'Geschäft' comes from the verb 'schaffen' (to manage/create/accomplish). It therefore refers to something that one 'schafft' (does or accomplishes)—whether a trade, work in a shop, or another activity.
Er hat es geschafft, ein erfolgreiches Geschäft aufzubauen.
He managed to build a successful business.
The plural 'die Geschäfte' can be ambiguous. It can mean 'shops' or 'business activities/transactions'. The context makes clear what is meant: 'Die Geschäfte in der Innenstadt' refers to shops, while 'Die Geschäfte laufen gut' refers to economic success.
Am Sonntag sind die Geschäfte in Deutschland geschlossen.
On Sundays, the shops in Germany are closed.
When 'Geschäft' means a shop, it is often combined with the verbs 'führen' (to run), 'eröffnen' (to open), or 'schließen' (to close). Movement toward a shop is expressed with 'ins Geschäft gehen' (to go to the shop).
Sie führt ein kleines Geschäft für Bioprodukte.
She runs a small shop for organic products.
In the meaning 'trade' or 'transaction', the typical verbs are 'ein Geschäft machen' (to make a deal) or 'ein Geschäft abschließen' (to close a deal). It is often combined with adjectives such as 'gut' (good) or 'schlecht' (bad).
Mit dem Verkauf des alten Autos hat er ein gutes Geschäft gemacht.
He made a good deal by selling the old car.
The expression 'im Geschäft sein' means to work professionally in a particular industry or sector. It is often combined with the name of the industry, e.g. 'im Musikgeschäft' (in the music business).
Mein Onkel ist seit über 30 Jahren im Autogeschäft.
My uncle has been in the car business for over 30 years.
The expression 'sein Geschäft machen/verrichten' is a euphemism, meaning a softened way to describe going to the toilet. It is used to address the topic indirectly and less bluntly.
Wir müssen kurz anhalten, der Hund muss mal sein Geschäft machen.
We need to stop briefly; the dog needs to do its business.
company / undertaking
'das Unternehmen' and 'das Geschäft' can both have to do with business and work. 'das Unternehmen' usually means the whole organization, that is, a company with employees, management, and tasks. 'das Geschäft' can be a shop, a single deal, or business activity in general. Learners can easily confuse the words because in German you talk about the 'Geschäfte' of a company. If you mean the company as an organization, 'Unternehmen' fits better. If you mean a shop, a deal, or ongoing trading/business activity, 'Geschäft' is more natural.

Am Samstag ist das kleine Geschäft in der Hauptstraße besonders voll.
On Saturdays, the small shop on the main street is especially crowded.
Das Unternehmen sucht neue Mitarbeiter für den Kundenservice.
The company is looking for new employees for customer service.