
*ER & IR Verbs share the same endings in the preterit tense.
*The endings of the “nosotros” forms of “AR” & “IR” verbs are the same in the preterit as in the present tense.
Sentences using subject pronouns with the verb HABLAR (To Speak) in the preterit tense:
-Yo hablé español bien, which means, I spoke Spanish well.
-Tú hablaste español bien, which means, You spoke Spanish well.
-Él/Ella/Usted habló español bien, which means, He/She/You spoke Spanish well.
-Nosotros hablamos español bien, which means, We spoke Spanish well.
-Vosotros hablasteis español bien, which means, You spoke Spanish well.
-Ellos/Ellas/Ustedes hablaron español bien, which means, They/You spoke Spanish well.
Stem Changing Verbs
Stem-changing AR and ER verbs are conjugated as regular verbs in the preterit tense. Some stem-changing IR verbs are conjugated as regular verbs in the preterit tense but others are changed when conjugated in the preterit tense in the third person singular and plural (Él/Ella/Usted & Ellos/Ellas/Ustedes). For example:

Spelling-Changing Verbs
Some Verbs change in spelling to preserve the sound of the infinitive.
1. Verbs ending in GAR, CAR & ZAR change only in the first-person singular (Yo).
2. There are two types of changes that occur in verbs with stems ending in vowels in the third person singular and plural (Él/Ella/Usted & Ellos/Ellas/Ustedes).
(a)Some of these verbs have a “y” inserted between two vowels.
Note: The Preterit Tense is used to express anything (actions, states, series of events etc) finished in the past.
Example:
1.El año pasado mi hermano cumplió doce años. – Last year my brother was 12 years old. / Last year my brother turned 12.
2.Fuimos ayer mis amigos y yo a la playa. – Yesterday my friends and I went to the beach.
3.Ya leí ese libro. – I already read that book.
Irregular Verbs
Irregular verbs are not all modified the same way in the preterit tense and there isn’t really any set rule, knowing the right modifications for irregular verbs will come by memorizing, reading articles in the preterit tense and using irregular verbs in composition writing.
Below are lists of some irregular verbs and their modifications:

These verbs are modified differently in the “Ellos/Ellas/Ustedes” form:

These irregular verbs are completely modified: