要 meaning “should”

要 can often be somewhat ambiguous as to whether it expresses “need” or “should”. Have a look at the example sentences below; you could interpret them as meaning “need” or “should” in English, but all of them use 要 in Chinese.

葡萄要先洗一洗再吃。

Pútáo yào xiān xǐ yī xǐ zài chī.

We should wash the grapes before we eat them.

生病时要多喝水。

Shēngbìng shí yào duō hē shuǐ.

You should drink more water when you're ill.

你学习中文要努力一点。

Nǐ xuéxí Zhōngwén yào nǔlì yīdiǎn.

You should put more effort into studying Chinese.

Often, 需要 is used to unambiguously express “need”. A lot of the time, though, the two concepts are not fully distinguished in Chinese sentences.