Spanish has several verb tenses to express the past; two of them are Pretérito Perfecto Compuesto (present perfect simple) and Pretérito Perfecto Simple (simple past). This is how to distinguish them:

Pretérito Perfecto Compuesto is normally accompanied by expressions that refer to the present time. The reason for this is that this tense describes a perfect (finished) action that was completed within the same time frame the speaker is talking from. This is a subjective measure, and can change depending on the speaker’s perspective, according to how relevant the past action is in today’s world.

Hoy (today)
Esta mañana (this morning)
Esta semana (this week)
Este mes (this month)
Este verano (this summer)                               he estado en Buenos Aires.
Nunca (never)
Ya (already, yet)
Todavía no (not yet)

Pretérito Perfecto Simple can be accompanied by past time expressions that are not related to the present. It is a finished action that was completed in a time frame that is different to the one the speaker is talking from (again, subjectively). Therefore, the action is not relevant today.

Ayer (yesterday)
Hace cinco años (five years ago)
El mes pasado (Last month)
La semana pasada (last week)                           estuve en Buenos Aires.
El 4 de enero de 1989 (January 4th, 1989)
Hace mucho tiempo (a long time ago)
Cuando era pequeño (when I was a child)

If you have any questions about this, don’t hesitate to post a comment.

See you next time!