To conjugate verbs in the preterite tense you just have to remove the infinitive endings and add the correct preterit ending depending on who the subjects of the action is. You already know the different verb endings ar ir and er. ir and er verbs have the same preterite endings
The different subjects are
1.yo
2. tú
3.usted, él, ella
4. nosotros
5. vosotros
6. ustedes, ellos, ellas
For ar verbs yo would drop the ar and add the ending accordingly so for
1. Yo the ending would change to -é
2. tú the ending would change to -aste
3. usted, él, ella the ending would change to -ó
4. nosotros the ending would change to -amos
5. vosotros the ending would change to -asteis
6. ustedes, ellos, ella, the ending would change to -aron
For the ir and er verbs, you would drop the ir or er and add
1. Yo the ending would change to -í
2. tú the ending would change to -iste
3. usted, él, ella the ending would change to -ió
4. nosotros the ending woul change to - imos
5. vosotros the ending would change to -isteis
6. ustedes, ellos, ellas the ending would change to -ieron
An example would be an ar verb viajar
1. Yo viajé
2. Tú viajaste
3. Él (ella, ud.) viajó
4. Nosotros viajamos
5. Vosotros viajasteis
6. Ellos (ellas, uds.) viajaron
