比赛开始了。

Bǐsài kāishǐ le.

The competition has begun.

我才刚刚开始学汉语。

Wǒ cái gānggāng kāishǐ xué Hànyǔ.

I have just started learning Mandarin.

好，计时开始！

Hǎo, jìshí kāishǐ!

OK, the timer has started!