The German verb bauen means "to build" or "to contruct" and is generally used for physical structures, though not exclusively. 

Ihre Kugelnester baut sie gern auf halber Höhe über dem Wasser.

It likes to build its spherical nests halfway up above the water.

Caption 36, Die letzten Paradiese: Die Schönheit der Alpen 1

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Verbs that consist of bauen and a prefix follow a similar pattern. The verb aufbauen, for example, can refer to setting something up, but also restructuring something. Note the phrase neu aufbauen as well, as this means "to restructure" or "to reestablish."

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Alles hängt zusammen und muss verbessert oder gar ganz neu aufgebaut werden.

Everything is connected and must be improved or even completely rebuilt.

Caption 15, 30 Jahre: Menschen für Menschen

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Emma würde sehr gerne mit ihren Freunden nächste Woche auf dem Kirchenbasar einen Flohmarktstand aufbauen.

Emma would very much like to set up a flea market stand with her friends at the church bazaar next week.

Captions 41-42, Die Pfefferkörner: Endspurt

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When a building is renovated or something is physically converted or modified, the verb umbauen is often used: 

Damit der A dreihundertachtzig überhaupt in Frankfurt landen kann, musste die Fraport AG so einiges umbauen.

In order for the A three hundred and eighty to even be able to land in Frankfurt, Fraport AG had to rebuild quite a few things.

Captions 38-39, Rund um den Flughafen: Der neue Airbus A-380

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The verb einbauen is generally translated as "to install":

Ne, wenn man hier Magnete einbauen würde, so dass das Dodomobil leicht über dem Boden schwebt, dann wäre da keine Reibung.

Right, if you were to install magnets here, so that the Dodomobile gently floats above the ground, then there would be no friction.

Captions 69-71, Das 1. Newtonsche Gesetz: erklärt am Beispiel des Dodomobils

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The verb nachbauen has the connotation of copying something:

Das sind Menschen, die einfach das Original im Kleinen nachbauen möchten.

These are people who simply would like to reconstruct the original on a small scale.

Caption 5, Modelleisenbahner: Mehr als nur ein Hobby

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The verb anbauen refers to agriculture and the act of planting, growing, or cultivating. 

Außerdem sollen Lebensmittel ökologisch angebaut werden.

In addition, food should be organically grown.

Caption 25, Erklärvideos: Nachhaltigkeit einfach erklärt

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And finally, the verb abbauen means to dismantle, dissolved, or reduce. When something is biologisch abbaubar, it means it's biodegradable. 

Das ist auch hundert Prozent ökologisch abbaubar.

That's also one hundred percent biodegradable.

Caption 26, Lerchenberg: Du bist, was du isst

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Further Learning
Try to create your own sentences with these verbs, or look for additional examples on Yabla German.

The verb erklären has two very different meanings, as does its noun form die Erklärung. One word having multiple meanings seems to happen more often in German than in English, if only for the fact that the German language has far fewer words than English. With fewer words in a language, it's more likely that a single word will have multiple meanings than in a language with a larger vocabulary!

The most common meaning of erklären is "to explain":

Kann jemand erklären, was ein Binnenhafen ist?

Can someone explain what an inland port is?

Caption 27, Bundesländer und ihre Rezepte: Nordrhein-Westfalen

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Wir erklären euch, wie man in Deutschland Ostern feiert.

We'll explain to you how you celebrate Easter in Germany.

Caption 3, Cettina und Sabine: Ostern

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And the same applies to its noun form, die Erklärung:

Vielleicht gibt's eine einfache Erklärung für seine Angst.

Perhaps there's a simple explanation for his fear.

Caption 62, Großstadtrevier: Von Monstern und Mördern

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Es braucht Erklärungen, um die Brutalität und Banalität des Unrechts zu verstehen.

Explanations are required to grasp the brutality and banality of this injustice.

Caption 19, DDR zum Anfassen: Ganz tief im Westen

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However, the second most common meaning of the verb erklären (and its noun equivalent die Erklärung) is as follows:

Kein Problem mehr für die Bewohner vor Ort, erklären sie stolz.

No problem anymore for the local residents, they declare proudly.

Caption 20, 30 Jahre: Menschen für Menschen

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Ich erkläre hiermit, dass Sinus einem Tierheim übergeben wird.

I hereby declare that Sinus will be handed over to a shelter.

Caption 70, Yabla Gerichtshof: Das verzogene Hündchen

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Note that the noun die Erklärung, when used with the meaning "declaration," is often paired with another noun as the latter half of a compound noun:

Jetzt also die Liebeserklärung an das Meer.

So now, the declaration of love for the sea.

Caption 26, Herbert Grönemeyer: stellt sein neues Album vor

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Eine entsprechende Absichtserklärung zwischen der People's Bank of China und der Deutschen Bundesbank wurde am vergangenen Freitag in Berlin unterzeichnet.

A corresponding declaration of intent between the People's Bank of China and the German Federal Bank was signed last Friday in Berlin.

Captions 3-4, Frankfurt wird Handelszentrum: für die chinesische Währung Yuan

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There are a number of German verbs nouns for "declare," such as the rather obvious deklarieren and the less obvious verkünden. Some nouns using die Erklärung as "to declare," such as die Kriegserklärung, also have words with similar meanings, such as die Kampfansage. Both of these words mean "declaration of war," something we've all seen far too much of in the last several years.

Further Learning
Luckily, in real-world usage, it's usually quite easy to tell by the context in which the words are used if the meaning "to explain" (explanation) or the meaning "to declare" (declaration) is intended. For details of the verb's conjugation, see this video about erklären on Yabla German.