你一定要鼓起勇气。

You must build up your courage.

Source: Tatoeba

Sentence Composition

=1 你 nǐ you (informal, as opposed to courteous 您 nín)
=1 你 nǐ you (Note: In Taiwan, 妳 is used to address females, but in mainland China, it is not commonly used. Instead, 你 is used to address both males and females.)
2 一定要 yīdìngyào must
3 鼓起勇气 gǔqǐyǒngqì to summon one's courage