When students first learn 就 (jiù), they're told that it means "just". But *just* like in English, the word "just" has many meanings and ways to use it. Here are 5 different ways to use "jiu" at level HSK 2 and 3.
1. Emphasize a Verb
Put "jiu" before a verb to emphasize the verb.
Michael shì shéi? jiù shì wǒ.
Who is Michael? It's me.
2. An Action Takes a Short Time
Tiān'ānmén guǎngchǎng lí zhèr bù yuǎn, zǒulù èrshí fēnzhōng jiù dào le.
Tian'anmen Square is not far from here. It just took 20 minutes to walk there.
3. An Action Will Happen Soon
This is the most common meaning of "jiu" in HSK 2 textbooks.
Děng wǒ yīxià, wǒ jiù lái.
Wait for me, I will come soon.
The struture "jiu...le / jiuyao... le" is the same meaning.
Chūnjié jiùyào lái le.
The Spring Festival is coming soon.
4. An Action Happened Earlier Than Expected
In this case, put "jiu" after the time word.
Wǒ zǎoshang 8 diǎn jiù dào gōngsī le.
I arrived the company at 8 am.
5. Then, As a Conjunction
Zhǐyào nǐ nǔlì xuéxí, nǐ jiù yīdìng néng chénggōng.
As long as you study hard, then you will surely succeed.
The structure "...le...jiu..." has the same meaning but indicates two actions occurred successively.
Zuótiān wǒ huíle jiā jiù shuìjiào.
Yesterday I went home then slept immediately.
These are 5 different mearnings of "jiu" in HSK 2 and 3. Why are there so many variations at an elementary level? Maybe because it's commonly used in every day conversation. Hope this helps you understand it a little better.