This expression indicates that one has an obligation or has promised to do something. Put なければ なりません after Vない. Vない refers to what is left after dropping the ない ending of the Nai-form of a verb.
Cf. See Lesson 9-1 for the formation of the Nai-form of verbs.
外国旅行の 時、パスポートを もって 行かなければ なりません。
You must take your passport with you when traveling abroad.
いつも けんこうに ちゅういしなければ なりません。
We always have to be careful about our health.