The passive voice is used to put the focus of a sentence on the object or the action, and often avoid naming the subject at all. The formation of the German passive voice can be quite confusing, so let's go step by step. 

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The Vorgangspassiv is formed with the verb werden, which in these cases is not translated as "to become," but instead as "to be." These sentences answer the question of "What is being done [to X]?" The sentences below have the following structure: 

Conjugation of werden + past participle

Notice that in the first sentence, the question of who is carrying out the action (making sauerkraut out of cabbage) is left completely unanswered. This is actually the case in the third sentence as well. However, as you can see in the second example, the subject (die Ereignisse) can still be integrated into a sentence in the passive voice by using the preposition von.

Es wird aus Kohl gemacht und es schmeckt sauer.

It is made from cabbage and it tastes sour.

Caption 30, Deutsch mit Eylin: Denk schnell!

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Große Erfindungen werden oft von ungewöhnlichen Ereignissen inspiriert.

Great inventions are often inspired by unusual events.

Caption 3, 200. Geburtstag: Die Geschichte des Fahrrads in 2 Minuten

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Mit dem Handscanner wird jeder Koffer erfasst.

Every suitcase is registered with the handheld scanner.

Caption 40, Ab in den Urlaub: So kommt der Koffer in den Flieger

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A more complex structure is necessary when we ask, for example, "What is/was allowed to be done [to X]?", "What should be done to [X]?", or "What must be done [to X]?" Now werden is kept in the infinitive, and it is the modal verb that is conjugated. The structure for this is: 

Conjugated modal verb + past participle + werden

Erst nach seinem Jahrestag im August durfte hier gefischt werden.

Only after its anniversary in August was fishing allowed here.

Caption 8, Alpenseen: Kühle Schönheiten

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Außerdem sollen Lebensmittel ökologisch angebaut werden.

In addition, food should be organically grown.

Caption 25, Erklärvideos Nachhaltigkeit einfach erklärt

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Das heißt also, dass auch das Adjektiv dekliniert werden muss.

So this means that the adjective must also be declined.

Caption 64, Deutsch mit Eylin: Die 4 Fälle

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Further Learning
Try to remove the subject and re-construct these simple sentences using the Vorgangspassiv. Clicking on the sentence will take you to the Yabla German video that contains the answer!

1. Die Leute essen das Gericht gerne mit Kartoffelpüree.

2. Nun muss ich die Äpfel schälen und schneiden.

3. Er muss die Maske überall tragen.