The subjunctive mood is used primarily in dependent clauses, it is also used in certain circumstances to express necessity or obligation

es necesario, es preciso, hace falta que, etc.

Es preciso que vaya a la universidad.
It is necessary that you go to the university.

Es preciso que le hables.
It's necessary that you talk to him.

Es menester que lo veas.
It's necessary that you see it.

Es preciso que trabaje.
It is necessary that you work.

Es necesario que usted coma.
It is necessary that you eat.

Es necesario que reposes bien.
It is necessary that you get good rest.

Es necesario que solicite un visado.
It's necessary that he applies for a visa.