从 + 那时 + 起
那时 (nàshí) means "that time" or "at that moment" and is used to refer to a specific point in the past. It is commonly combined with 起 (qǐ) in the phrase 从那时起 meaning "from that time on." This phrase marks the starting point of a change or ongoing state.
那时我才十岁,什么都不懂。
Nà shí wǒ cái shí suì, shénme dōu bù dǒng.
At that time I was only ten years old and didn't understand anything.
从那时起,他就下定决心要学好中文。
Cóng nà shí qǐ, tā jiù xià dìng juéxīn yào xué hǎo Zhōngwén.
From that time on, he made up his mind to learn Chinese well.
那时的北京还没有这么多高楼。
Nà shí de Běijīng hái méiyǒu zhème duō gāolóu.
At that time, Beijing didn't have this many tall buildings.