In Spanish, there are two key past tenses: the preterite and the imperfect. Each one has a special role.

Preterite:

• What it does: It is used for actions that are completed.
• Example: "Ayer comí pizza."
  (This means "Yesterday, I ate pizza.")

Imperfect:

• What it does: It talks about actions that were happening or ones that happened regularly in the past.
• Example: "Cuando era niño, siempre comía pizza."
  (This means "When I was a child, I always ate pizza.")

Using Both Tenses Together:

Sometimes, to tell a more exciting story about the past, you can use both tenses.

You use the preterite for actions that were completed and the imperfect for background information or descriptions.

Example: "Mientras yo estudiaba (imperfect) en casa, mi amigo llamó (preterite)."
(This means "While I was studying at home, my friend called.")

Combining these tenses makes your story more interesting and gives more details about what was happening.