I have just finished the chapter 3 of "La pequeña Ariadna" (the rest of the chapters are available at this very webpage on Text to Practice). You can learn the use of the perfect tense there. Remember that it is used when the sentence occurs during the present and the actions have a perfect aspect (finished actions). Later we will see that there are better ways to write instead of using only the perfect tense. This is just to make it easier for you to get the concept.
At your service, as always =)