The verb expression hay que can be used to indicate obligation. When talking about the present we use the formula hay + que + infinitive

Let's look at some example sentences:

Hay que estudiar.
It's necessary to study.

Hay que denunciar el robo.
It's necessary to report the thief.

Hay que recoger unos libros.
It's necessary to collect some books.

Hay que preparar el examen.
It's necessary to prepare the exam.

Hay que reservar los asientos.
It's necessary to reserve the seats.

When talking about the past we usually use the formula había + que + infinitive

Había que cerrar el portón.
It was necessary to close the gate.

Había que pagar la mensualidad.
It was necessary to pay the monthly fee.

Había que comprar vegetales.
It was necessary to buy vegetables.

Había que tomar precauciones.
It was necessary to take precautions.