穿西装不一定要系领带。

Chuān xīzhuāng bù yídìng yào jì lǐngdài.

It isn't always necessary to wear a tie when wearing a suit.

我不懂怎么系领带。

Wǒ bù dǒng zěnme jì lǐngdài.

I don't know how to tie a tie.

出席重要的场合还是系领带比较好。

Chūxí zhòngyào de chǎnghé háishì jì lǐngdài bǐjiào hǎo.

It's better to wear a tie when attending important occasions.