For verbs ending in -ar the following endings should be added to the stem of the verb (a practical example is provided in the brackets):
-é (hablé)
-aste (hablaste)
-ó (habló).
-amos (hablamos).
-asteis (hablasteis).
-aron (hablaron).
-er and -ir verbs have the same endings, which are as follows:
-í (viví).
-iste (viviste).
-ió (vivió).
-imos (vivimos).
-isteis (vivisteis).
-ieron (vivieron).
The Preterite Tense is generally used in 6 different situations which are listed below.
2) When referring to actions that occured a specific number of times.
Eg. I called you 3 times.
3) When talking about things that happened in an enclosed period of time.
Eg. He went on holiday for 2 months.
4) Actions that are part of a chain of events.
Eg. I ate breakfast, packed my bag, and went to school.
5) When describing sudden changes in sentiment or opinion.
Eg. In that moment, I was extremely angry.
6) Used in phrases that pin point a particular time. Key words to look out for are "yesterday," "last night," "afterwards," "last year," "the other day," etc...
[The verbs in italics are the ones that would be in the preterite tense if the sentence was in Spanish. I just thought that it would be easier to understand the context in which they are used if you could see it in English].
I would be happy to look at practise examples in Spanish and tell you if you are on the right track.
This tense also has a lot of irregular verbs, which I suggest you memorize as soon as possible as they don't follow a specific rule in their irregularity.