In Spanish we use four verb tenses in Indicative mode to talk about the past. In this infographic I leave you how the Indefinite Preterite (Pretérito Indefinido in Spanish) is conjugated, the equivalent in some cases to the  past simple in English.

My recommendation, as Spanish tutor, to  not to be wrong when using this verb tense is to remember the “time markers”.

I hope it helps you.