在 Zài, which comes before the verb denotes a ‘action in progress’:
我在上中文课。Wǒ zài shàng zhōngwén kè. (I am taking Chinese class.)
我在学挪威语。Wǒ zàixué nuówēi yǔ. (I am learning Norwegian.)
我在上班。Wǒ zài shàngbān. (I’m working now.)
正 Zhèng ‘just’ is regularly used with 在 zài makes the sentence a little more emphatic:
他们正在打球。Tāmen zhèngzài dǎqiú. (They are playing ball.)
他正在工作。Tā zhèngzài gōngzuò. (He is working.)
弟弟正在玩电脑游戏。Dìdì zhèngzài wán diànnǎo yóuxì. (The younger brother is playing computer games.)
The sentence particle 呢 ne may be used to introduce a tone of mild assertion into ‘action-in-progress’ sentences:
他正在上班呢。Tā zhèngzài shàngbān ne. (He is at work.)
我正在度假呢。Wǒ zhèngzài dùjià ne. (I’m on vacation.)
妹妹正在学习呢。Mèimei zhèngzài xuéxí ne. (My sister is studying.)
在 Zài can refer to defined time periods other than the present:
我最近在准备考试。Wǒ zuìjìn zài zhǔnbèi kǎoshì. (I’m preparing for an exam recently. )
我去年在学中文呢。Wǒ qùnián zàixué zhōngwén ne. (I was learning Chinese last year. )
上周我在旅游。Shàng zhōu wǒ zài lǚyóu. (I was traveling last week.)
A frequency adverb can also be used to express ongoing or persistent ‘action in progress:
他每天晚上都在学中文。Tā měitiān wǎnshàng dū zàixué zhōngwén. (He studies Chinese every night.)
我天天都在加班。Wǒ tiāntiān dū zài jiābān. (I work overtime every day.)
每个中午他都在抽烟。Měi gè zhōngwǔ tā dōu zài chōuyān. (He smokes every noon.)
在 zài indicates location or place.
For example:
王老师在办公室.Wáng lǎoshī zài bàngōngshì. (Teacher Wang is in the office.)
我在挪威。Wǒ zài Nuówēi. (I am in Norway.)
他们在广州。Tāmen zài Guǎngzhōu. (They are in Guangzhou.)
我妈妈在家。Wǒ māmā zài jiā. (My mother is at home.)
我们在学校打球。Wǒmen zài xuéxiào dǎqiú. (We play ball at school.)
The adverb 不 bù is placed before the verb 在 zài to create the negative form of 在 zài. Keep this in mind when preceding a fourth tone, the character “不” bù is pronounced as a second tone bú.
For example:
王老师不在办公室.Wáng lǎoshī búzài bàngōngshì. (Teacher Wang is not in the office.)
我不在挪威。Wǒ búzài Nuówēi. (I am not in Norway.)
他们在广州。Tāmen búzài Guǎngzhōu. (They are not in Guangzhou.)
我妈妈不在家。Wǒ māmā bú zài jiā. (My mother is not at home.)
我们不在学校打球。Wǒmen búzài xuéxiào dǎqiú. (We don’t play ball at school.)
