Saber (to know) is irregular in the preterite.
We use saber when we know facts, know from memory, or know how to do something.

El supo que yo no supe cocinar.
      He knew that I did not know how to cook.

¿Cuándo supiste la verdad?
      When did you know the truth?

Usted supo que el boxeador está muy grave.
      You knew that the boxer is in very serious
       condition.

Supimos quién ganó enseguida.
      We knew who won right away.

No supisteis convencerla.
      You guys didn't know how to convince her.
         (used in Spain)

Ustedes tuvieron la oportunidad y no supieron
       aprovecharla.
     You guys (formal) had the opportunity and did
        not know how to take advantage of it.