To know = Saber

THE PRETERITE (Supe)

Generally, the preterite is used for completed actions (actions that have definite beginning and end points.) These can be actions that can be viewed as single events, actions that were part of a chain of events or actions that specifically state the beginning and end of an action.

Examples:

Mis amigos estaban asombrados porque SUPE la respuesta cuando el maestro hizo la pregunta.

My friends were amazed because I KNEW the answer when the teacher asked the question.

SUPE que Jim está enfermo.

I found out that Jim is sick.

Fui al baile anoche.

I went to the dance last night.

THE IMPERFECT (Sabía)

The imperfect tense is generally used for actions in the past that do not have a definite end. These can be actions that are not yet completed or refer to a time in general in the past. It can also be used to talk about:

   -actions that were repeated habitually

   -actions that set the stage for another past tense event

   -time and dates

   -a person’s age in the past

   -characteristics

  -mental or physical states

Examples:

SABÍA que ganaría la competencia.

I KNEW that I would win the competition.

Cuando era niña, jugaba con muñecas.

When I was a child, I used to play with dolls.

DIFFERENCE BETWEEN "Supe" and "Sabía"

They actually have the same verbal meaning, but their use differs when mentioning that one knowledge (sabía) was "CONTINUOUS" or "PERMANENT", while the other (supe) is given AT A SPECIFIC MOMENT.

SUPE que Jim está enfermo.

I found out that Jim is sick. (At a specific moment you found out that)

SABÍA que ganaría la competencia

I KNEW that I would win the competition. (The knowledge that I would be the winner was there since before the competition. Although we do not know exaclty since when)

When someone gives/tells you the information/knowledge, it is better to use "Supe que/Me enteré de que."

When you discover something by yourself, it is better to use "Descubrí que."

I hope this helps.

Hey David. Ya lo sabía, Yo lo supe todo este tiempo. I consulted on a page and I could find this

The choice between the simple or indefinite past perfect (supe) and the imperfect (sabía) assumes that, in the first case, the action occurs at a specific moment in the past, as a finished, closed action; in the second, on the other hand, that verbal action cannot be located at an exact point in time, but is presented in development, unfinished, or as a description of reality.

By the way, "Saber" is also for flavor, "taste".

Ella sabe mucho sobre matemáticas. "to know"

La arepa sabe riquísimo. "to taste"

I hope it works for you