我听不懂你在说什么。

Wǒ tīng bù dǒng nǐ zài shuō shénme.

I don't understand what you're saying.

我懂说一点普通话。

Wǒ dǒng shuō yìdiǎn Pǔtōnghuà.

I know how to speak a little Mandarin.

我怕考试的时候看不懂。

Wǒ pà kǎoshì de shíhou kànbudǒng.

I'm afraid I won't understand during the exam.