How do you conjugate regular verbs into the preterite?

The preterite tense is used for actions that are carried out as a one off-action, in the past. For example, one could be saying 'I spoke', 'I ate', or 'we sang'. In order to conhugate these verbs you need to follow the pattern for AR verbs, and then a different pattern for regular ER and IR verbs.

For AR verbs, the stem is kept, and then is conjugated like this

YO CANT-É TÚ CANT-ASTE ÉL CANT-Ó NOSOTROS CANT-AMOS VOSOTROS CANT-ASTEIS ELLOS CANT-ARON

FOR ER and IR verbs, the pattern is as such.

YO VIV-Í TÚ VIV-ISTE ÉL VIV-IÓ NOSOTROS VIV-IMOS VOSOTROS VIV-ISTEIS ELLOS VIV-IERON.

The same rule follows for ER verbs as for IR verbs.