Expresses the necessity or obligation; 'must', 'have to'.
The ～なくてはいけない grammar point is used to express the necessity or obligation to do something. It can be translated as 'must' or 'have to' in English. The formation requires the negative form of a verb and is followed by いけない (cannot go/progress). It indicates that if something is not done, it will be a problem or inappropriate.