である (or
であります) is a construction in Japanese that is considered to be the formal equivalent of
だ. This should not be confused with the 丁寧語（ていねいご） (polite language) word,
です, as
である is simply a combination of the 連用形（れんようけい） (conjunctive form) of
だ, and the う - Verb, ある.
である may be used in any place that
だ would usually be used, but is most likely to be found at the end of sentences/statements.
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日本一（にほんいち）デカい博物館（はくぶつかん）はこの博物館（はくぶつかん）である。
The largest museum in Japan is this one.
ここから悲（かな）しいことが起（お）きるのである。
This is where something sad starts to happen. (Here comes the sad bit)
私達（わたしたち）が会（あ）えたのは運命（うんめい）であります。
It is destiny that we met.
Because the な that is used with
な-Adjectives is simply the 連体形（れんたいけい） (attributive form) of
だ,
である may replace な or の when connecting one noun to another. The attributive form just means the form of a word that can be directly linked to a noun. As ある’s 連体形（れんたいけい） is just ある, it does not need to be modifed at all.
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大変（たいへん）であることを人（ひと）にやらせるのは良（よ）くない。
It is not good to make someone else do difficult things.
重要（じゅうよう）である箇所（かしょ）をまとめた資料（しりょう）がこちらです。
These are the documents highlighting all the important sections.
However, although this is grammatically correct, it would sound quite stiff in many circumstances, and should be avoided in standard speech.
であります (as opposed to
である) is very formal, and will almost exclusively be used by people within jobs that absolutely require this level of formality (politics, police force, military, etc). Due to this, its use within regular conversation will sound stiff, or perhaps even like the speaker is jokingly being over polite.
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名前（なまえ）はタナカであります！
My name is Tanaka! (Responding to a person in a higher rank in a military)
最後（さいご）のプリンを食（た）べたのは私（わたし）であります。
I am the one who ate the last pudding. (Jokingly polite)