Meaning of gāi:
该
should; ought to; must be; to deserve; to owe; to be sb's turn to do sth
Nǐ gāi zǎodiǎn xiūxi.
你该早点休息。
You should rest early.
Wǒmen gāi zǎodiǎn chūfā, yǐ bìmiǎn jiāotōng yōngdǔ.
我们该早点出发，以避免交通拥堵。
We ought to set off earlier to avoid traffic congestion.
Nǐ gāi qù kàn yīshēng le.
你该去看医生了。
You should go see a doctor.
Tā gāi dédào jiǎnglì.
他该得到奖励。
He deserves to get a reward.
Wǒ xiǎng zhīdào wǒ gāi huán duōshǎo zuòyè.
我想知道我该还多少作业。
I want to know how much homework I owe.
Xiànzài gāi nǐ shuō le.
现在该你说了。
Now it's your turn to speak.
probably
Tā gāi yǐjīng dàojiā le.
他该已经到家了。
He has probably already arrived home.
that; the above-mentioned
Gāi shū yǐjīng jiè chūqù le.
该书已经借出去了。
That book has already been borrowed.
Gāi wénjiàn xūyào zài míngtiān zhīqián tíjiāo.
该文件需要在明天之前提交。
The above-mentioned document needs to be submitted before tomorrow.
