What is the difference between the perfect tense and the preterite tense?

The preterite and perfect tenses are both used when an action has been completed. Then, what is the difference? Well, their use depends on regional differences and varieties of Spanish. But don't panick! It is actually simpler than it seems. 1.) In most of Latin America, when an action is completed, only the preterite is used, regardless of when it happened. E.g. "Hoy salí a correr" (I went for a run today). E.g. "Ayer no fui al colegio" (I didn't go to school yesterday). 2.) In most of Spain, when an action is completed, we need to look at when that action happened. a) If the completed action happened yesterday or before yesterday, we use the preterite tense. E.g. "Ayer comí tarta" (I ate cake yesterday). E.g. "Hace dos años fui a Inglaterra" (I went to England two years ago). b) If the completed action happened today, we use the perfect tense. E.g. "Hoy he salido a correr" (I went for a run today). Notice how I used the very first example again, but with a different verb tense. As you can see, there is more than one way of expressing the same idea. However, they are both equally correct, so pick your favourite! (When it comes to identifying dialects/varieties of Spanish this is a very useful hint).