Can you give an example, please?

I think it matters on the language you are using. In Spanish preterit tense is used to refer to actions that occurred at a fixed point in time. In Hebrew grammar the imperfect tenses is used to refer to uncompleted action and describes a present or future time. You might have to look it up in a specific grammar book for the language you are studying.

If you are talking about Spanish, which is the language in which I learned these terms, the imperfect tense is used to describe something that happened in the past with no specifically stated time. For example, the sentence "When I was a young child, I went to the mall," when translated into Spanish would require you to conjugate the verbs "be" and "go" (used as "was" and "went" in English) to the imperfect tense.

The preterite tense is used to describe something that occurred in the past at a specific time. For example, the sentence "I went to the mall last Wednesday" when translated into Spanish would require you to conjugate the verb "go" (used as "went" in English) to the preterite tense.

Hope this helps.