です (desu) — sensushi

Related patterns3

である
Same copula slot, opposite register — です is the spoken and default written polite copula, である is its written-plain counterpart for essays, reports and rules, and a text mixing the two reads as a mistake.
でございます
でございます is です raised one step further, the copula a shop or receptionist uses toward a customer, where です stays the ordinary polite default among equals.

んです
です simply predicates (学生がくせいです), while んです wraps the same sentence as an explanation the listener needs (学生がくせいなんです) — dropping the ん loses that explanatory frame, and adding it where nothing needs explaining sounds odd.

states what something is — noun plus です

彼かれは山田やまだです。

kare wa yamada desu.

He is Yamada. neutral

本日ほんじつの司会しかいは田中たなかです。

honjitsu no shikai wa tanaka desu.

Today's moderator is Tanaka. formal

describes with a な-adjective — な-adjective stem plus です

この部屋へやは本当ほんとうに静しずかです。

kono heya wa hontou ni shizuka desu.

This room really is quiet. neutral

あの店みせの店員てんいんさんはとても親切しんせつです。

ano mise no ten'in-san wa totemo shinsetsu desu.

That shop's clerk is very kind. neutral

だdacolloquial
the plain copula — spoken among intimates and in written-plain prose alike (学生がくせいだ, 静しずかだ); です is what politeness puts in its place.

でしょう is です's own conjecture cell (明日あしたは雨あめでしょう。) — a
prediction offered on the speaker's authority, not a further politeness step.