Hola, Kloe:
The past simple or "pretérito indefinido" in Spanish, is normally used to talk about completed actions in the past. The auxiliar verb "haber" plus the past participle form the "pretérito perfecto", and it makes reference to actions that have a connection to the present. Normally, "pretérito indefinido" is used with time expressions like ayer, la semana pasada, el mes pasado, el año pasado, etc. While "pretérito perfecto" is used with expressions like hoy, esta mañana, esta tarde, esta noche, este mes, etc.