about 就：

— as a marker of uniqueness:

  我就认识他。wǒ jiù rèn shi tā 

  I just know him.

—as a marker of identification. In this sense it is often used to signal a location at the end of a series of directions.

 银行就在那儿。yín háng jiù zài nàr

The Bank is right there.

—as a marker of identification 就 may also signal that a person has been located.

A： 你找谁？  nǐ zhǎo shuí

B：我找马老师。 wǒ zhǎo mǎ lǎo shī 

A:我就是。 wǒ jiù shì 

你好！

Isn`t it used also in the “If…, then…” structure?

如果明天下雨，我就不去公园。

Correct! “if…, then…” structure also makes sense. e.g 
如果你努力，就能学好汉语！

you also hear “就是” that’s kinda like the english “du-uh,” “precisely,” “yeah-uh,” the kinds of confirmative responses to obvious statements, like if some kids thought up of a prank to spray graffiti on a school principle’s door, one kid might say, “but if we get caught, we’ll be put in detention,” and another kid will be like, “du-uh,” 就是, so obvious…

As an adverb, 就 (jiù) can be placed before the predicate to add emphasis. It often has an intense or provocative feel to it, similar to “just.” In English we might say, “it’s just not right!” This emphasis very often appears as 就是 in Chinese.

——就是 + Noun

Wǒmen jiùshì tā de jiārén.

我们就是 他 的 家人 。

We’re his family.

——Used as “Only Because”

Tā wèn zhème duō, jiùshì dānxīn nǐ.

她 问 这么 多，就是 担心 你 。

She asked so many questions only because she’s worried about you.