PAST SIMPLE

An action that started and finished in the past.

+: I did my homework last week
-: I did't do my homework last week
?: Did I do my homework last week?

PRESENT PERFECT 

An action that started in the past and it's connected to the present, because:

-It still continues: I have lived in Elche for 18 years.
-Experiencies (they will never be "eliminated"): Tom has seen a ghost.
-Consecuencies are in the present: The windowa are son clean because i have cleaned them.