Number + 年
年 (nián) as a measure of duration means "year" in the sense of a span of time. When preceded by a number, it expresses how many years, as in 三年 (three years). Unlike its use as a calendar year, this usage emphasizes the length of a time period rather than a specific point in time.
她在国外生活了五年。
Tā zài guówài shēnghuó le wǔ nián.
She lived abroad for five years.
我学中文已经两年了。
Wǒ xué Zhōngwén yǐjīng liǎng nián le.
I have been studying Chinese for two years.
这个工程预计需要三年才能完成。
Zhège gōngchéng yùjì xūyào sān nián cái néng wánchéng.
This project is expected to take three years to complete.