Usages of jiǔ
从 八 点 到 九 点 我 在 图书馆 学习。Cóng bā diǎn dào jiǔ diǎn wǒ zài túshūguǎn xuéxí.
From eight to nine, I study at the library.
我们 九 点 出发 吧。wǒmen jiǔ diǎn chūfā ba.
Let's set off at nine o'clock.
Elon.io is an online learning platform
We have an entire course teaching Chinese grammar and vocabulary.