liefern
to deliver
To bring goods, packages, or ordered items to a specific place or person.
Der Onlineshop liefert die Ware innerhalb von zwei Werktagen.
The online shop delivers the goods within two business days.

to deliver / provide
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to deliver
To bring goods, packages, or ordered items to a specific place or person.
Der Onlineshop liefert die Ware innerhalb von zwei Werktagen.
The online shop delivers the goods within two business days.

The verb 'liefern' (to deliver/provide) is very often used with two objects: a person in the dative (to whom something is delivered) and a thing in the accusative (what is delivered).
Der Lieferservice liefert uns das Essen direkt ins Büro.
The delivery service delivers the food directly to our office.
When it is about physical objects (package, pizza), the first meaning is intended. When it is about information (evidence, reasons), the second, abstract meaning is intended. The reflexive form 'sich etwas liefern' always points to a competition.
Die Polizei hofft, dass der Zeuge neue Hinweise liefern kann.
The police hope that the witness can provide new clues.
In the meaning of 'etwas bringen' (to bring something), 'liefern' (to deliver) is often combined with ordered goods. Typical phrases are 'Waren liefern' (to deliver goods), 'ein Paket liefern' (to deliver a package), or 'Essen nach Hause liefern lassen' (to have food delivered to your home).
Wir lassen uns die Getränke für die Party liefern.
We’re having the drinks for the party delivered.
Besides goods, 'liefern' (to provide) can also make abstract things available. Common combinations are 'Beweise liefern' (to provide evidence), 'Argumente liefern' (to provide arguments), 'eine Erklärung liefern' (to provide an explanation), or 'Ergebnisse liefern' (to deliver results).
Der Experte lieferte eine plausible Erklärung für das Phänomen.
The expert provided a plausible explanation for the phenomenon.
In the expression 'sich etwas liefern', the verb is reflexive with a dative pronoun (sich) and an accusative object. It describes a mutual contest or conflict.
Die beiden Teams lieferten sich ein spannendes Spiel.
The two teams had an exciting game.
to bring
'bringen' and 'liefern' can both mean that something comes to a person or to a place. 'bringen' is more general and fits many everyday things: you bring food, documents, or a friend home. 'liefern' is used especially for ordered goods, packages, or for things that someone expects, such as results or evidence. Learners may confuse the words because a delivery also involves bringing something. In practical terms: a person simply brings something along or takes it somewhere. A shop, a service, or a team delivers or provides something that has been ordered or is needed.

Der Supermarkt hat die Bestellung am Abend direkt zur Nachbarin geliefert.
The supermarket delivered the order directly to the neighbor in the evening.
Du bringst bitte die Getränke zur Feier mit.
Please bring the drinks to the party.