
und
and
Connects words, parts of a sentence, or sentences of equal rank; a listing or sequence.
Er kaufte Brot, Käse und Wein.
He bought bread, cheese, and wine.
and
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and
Connects words, parts of a sentence, or sentences of equal rank; a listing or sequence.
Er kaufte Brot, Käse und Wein.
He bought bread, cheese, and wine.

and
Expresses a sequence or consequence.
Sie lernte fleißig und bestand die Prüfung mit Bravour.
She studied hard and passed the exam with flying colors.

and
Used to connect two identical verbs or adjectives in order to express duration or intensity.
Sie wartete und wartete, aber er kam nicht.
She waited and waited, but he did not come.
The conjunction 'und' (and) connects two main clauses without changing the word order. The verb in the second clause stays in position 2 as usual.
Ich koche das Abendessen und mein Partner deckt den Tisch.
I am cooking dinner and my partner is setting the table.
'Und' (and) can connect almost all types of words or word groups of equal rank, not just whole sentences. This applies to nouns, adjectives, adverbs, or verbs.
Sie singt laut und falsch.
She sings loudly and off-key.
Although you learn in school not to begin sentences with 'und' (and), it is very common in spoken language and storytelling. It is used to keep the narrative flowing smoothly.
Wir gingen ins Kino. Und danach haben wir noch ein Eis gegessen.
We went to the movies. And afterward we had some ice cream.
To express a long duration or high intensity, you can repeat an adjective or verb with 'und' (and). This structure is very vivid and emotional.
Wir liefen und liefen, bis wir nicht mehr konnten.
We walked and walked until we couldn't go on anymore.
but
Und and aber can connect two statements that are valid at the same time. Aber explicitly marks the contrast between them; und merely joins them, so any surprising tension comes from the content alone. Choose aber when the contrast should be clearly emphasized.

Die Aufgabe ist schwierig, und Lisa löst sie schnell.
The task is difficult, and Lisa solves it quickly.
Die Aufgabe ist schwierig, aber Lisa löst sie schnell.
The task is difficult, but Lisa solves it quickly.