Quick explanation:
The words hubo and había are both used to express existence in the past. One in the preterite form and the other one in the imperfect form. We will see a few examples.

Hubo un accidente.
There was an accident.

Había catorce llaves en la mesa.
There were fourteen keys on the table.

Hubo más gente de la que invité.
There were more people than I invited.

Había un problema muy grave.
There was a very serious problem.

Long explanation:

Hubo
It is a simple preterite that expresses existence in the past and that is has been concluded.

Hubo un hombre en la guerra que no fue muerto.
There was a man in the war that was not killed.

En el concierto pasado hubo gran caos.
There was great chaos in the last concert.

No hubo ningún voluntario para repartir los volantes.
There wasn't any volunteer for the flyers delivery.

Hubo muchos problemas en la reunión.
There were many problems in the meeting.

Había

It is an imperfect preterite that expresses existence in the past with no reference to the time it started or ended.

Cuando entré a mi cuarto, había una araña enorme.
When I went into my room there was a huge spider.

Había mucha nieve en la carretera.
There was a lot of snow on the road.

Había dos o tres personas en la sala de espera.
There were two or three people in the waiting room.

En el museo había muchas piedras arqueológicas.
There were many archeological artifacts in the museum.

In all tenses, the third person singular ( él) form of the verb is used regardless of the number of what follows.

You may hear some Spanish speakers conjugate Haber in plural;

Habían muchos niños en el parque. - There were many children in the park.

This use is incorrect. Regardless of the number of objects present in the sentence, Haber is always conjugated in the third-person singular when functioning as a verb meaning "there was/ there were".