What is the different between Preterit and Imperfect verb tenses for Spanish? Any keywords for either one?

Answer 1

Actually. there are two main types of preterit; the perfect and the imperfect.

Perfect refers to an action already completed, ex: aprendí a escribir; crecí en Mexico; trabajé en España.

Imperfect refers to an action which ocurred in the past, but may happen again, ex: viajaba todos los días, conocía a todos, preguntaba lo que no sabía; pedía ayuda. I don't agree that it is also used to order, at least as far as i know

Answer 2

Verbs in the preterite tense indicate a completed action in the past.

Ayer escribí tres cartas.
Yesterday I wrote three letters.

Imperfect indicates a repetitive or incompeted action in the past.

Ayer escribia unas cartas.
Yesterday I was writing some letters.

Answer 3

I think you refer to preterit perfect and preterit imperfect. So, preterit means past tense.

If you use preterit perfect, you talk about a past totally finished
"Yo canté con este grupo" = I sang with this group (it's a past perfect, nowadays I don't sang with them)

And if you talk using Preterit Imperfect, you are talking about something that start in the past and you don't know when it was finished (similar to 'used to')
"Yo cantaba con este grupo" = I used to sing with this group (It's known that in past I sang with them, but nowadays, we cannot know if I continue doing it and from when...

Also the Imperfect is use with the verb 'querer' (want) as a formal way to order something
"Quería una cerveza" = I would like a beer