Time Duration + 前
The word 前 (qián) means 'before' or 'ago' when used in time expressions. It is placed after a time duration to indicate a point in the past, as in 三年前 (three years ago). It can also precede a noun to mean 'in front of' in spatial contexts.
三年前我在上海工作过。
Sān nián qián wǒ zài Shànghǎi gōngzuò guò.
I worked in Shanghai three years ago.
十分钟前他还在这里。
Shí fēnzhōng qián tā hái zài zhèlǐ.
He was still here ten minutes ago.
很久以前这里是一片森林。
Hěn jiǔ yǐqián zhèlǐ shì yí piàn sēnlín.
A long time ago, this place was a forest.