Sometimes things happen in a flash, or they happen a very short time before you say something, and to express that, you can use "刚" (gāng).

Structure:
"刚" expresses that the action happened not long ago. It's used the same way as "刚刚".

Examples:

Tā ɡānɡ zǒu.
他 刚 走。
He just left.

Wǒ ɡānɡ zuò wán jīntiān de ɡōnɡzuò.
我 刚 做 完 今天 的 工作。
I just finished today's work.

Structure:
"刚" can also express "from the time an action happens until the present time".

Examples:

Wǒ ɡānɡ dào zhèlǐ wǔ fēnzhōnɡ.
我 刚 到 这里 五 分钟。
I just got here five minutes ago.

Wǒ ɡānɡ lái zhōnɡɡuó bàn nián.
我 刚 来 中国 半 年。
I just got to China six months ago.