The verb haber has many uses. This lesson will focus on the use of haber to express existence - the "impersonal form" of haber. This form of haber has a special conjugation which doesn't reflect gender, person or number.
In the preterite tense, hubo is used to express there was or there were.
Hubo una explosión.
There was an explosion.
Hubo una tormenta de nieve anoche.
There was a snowstorm last night.
Hubo muchos invitados en el banquete.
There were a lot of guests at the banquet.
In the imperfect tense, había is used to express there was, there were, or there used to be.
Delante de nosotros había una mujer.
In front of us there was a woman.
Era un día muy bonito, no hacía calor y había una brisa muy fresca.
It was a nice day, it wasn't hot and there was a cool breeze.
Había unas treinta personas.
There were about thrity people.