zustellen
to deliver
To bring mail, parcels, or other shipments to the intended recipient.
Der Paketbote versucht, das Paket heute erneut zuzustellen.
The parcel carrier is trying to deliver the package again today.

to deliver / block
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to deliver
To bring mail, parcels, or other shipments to the intended recipient.
Der Paketbote versucht, das Paket heute erneut zuzustellen.
The parcel carrier is trying to deliver the package again today.

'Zustellen' (to deliver / block) is a separable verb. The prefix 'zu' comes at the end in a main clause. In subordinate clauses and in the infinitive with 'zu', the verb stays together.
Der Postbote stellt das Paket heute Vormittag zu.
The mail carrier is delivering the package this morning.
The meaning depends on the object. If it refers to 'Post' (mail), 'Pakete' (packages), or 'Briefe' (letters), it means 'to deliver'. If it refers to 'einen Weg' (a path), 'eine Tür' (a door), or 'eine Einfahrt' (a driveway), it means 'to block'.
Die Firma stellt wichtige Dokumente per Kurier zu.
The company delivers important documents by courier.
With 'zustellen' (to deliver), the person who receives something is often given in the dative. The item being delivered is in the accusative.
Der Bote hat mir heute Morgen einen Brief zugestellt.
The courier delivered a letter to me this morning.
When something is blocked, the object doing the blocking is often introduced with the preposition 'mit' (with). The structure is: etwas (accusative) mit etwas (dative) zustellen.
Du kannst den Flur nicht mit deinem Fahrrad zustellen.
You can't block the hallway with your bicycle.
to deliver / provide
'liefern' and 'zustellen' can both mean that a shipment or goods are brought to a person or a place. 'liefern' is more general and is especially suitable for ordered goods, food, or larger orders. 'zustellen' is used more for mail, packages, or official shipments when the recipient is supposed to receive the item. Learners may confuse the words because both have to do with transport. In practice: a shop liefert goods; a parcel service stellt ein Paket zu (delivers a package).

Der Brief wurde gestern an die neue Adresse zugestellt.
The letter was delivered to the new address yesterday.
Der Supermarkt liefert die Getränke morgen direkt zu uns nach Hause.
The supermarket will deliver the drinks directly to our home tomorrow.