We use the conjunction 故 in a compound sentence to express an effect or a result.
The first part of the compound sentence refers to the cause behind the result/effect. The second part of the sentence, which starts after the conjunction 故, refers to the result/effect.
We should state a comma before 故.
He has already adapted to life abroad, so he does not plan to return to the country
tā yǐjīng shìyìng le guówài de shēnghuó, gù bù dǎsuàn zài huíguó
I was delayed on the way, so I could not arrive on time
túzhōng yù shì dāngē, gù wèi néng ànqí dàodá
We usually use 故 in a structure with 因 , which indicates the reason something happens.
We had faith, so were able to win
yīn yǒu xìnxīn, gù néng zhànshèng
Because it’s not a decent thing to say, I won’t dare to say it
yīn bú shì tǐmiàn de shìqíng, gù bù gǎn shuōchūlái