For transitive verbs the modal verb for forming the present perfect is haben (to have). The modal verb haben is conjugated in present tense, and then the perfect participle is appended.

haben - the modal verb for transitive verbs   ich habe du hast er / sie / es hat wir haben ihr habt sie haben gegessen getrunken gekauft geklaut gelesen gebracht

sein - the modal verb for intransitive verbs   ich bin du bist er / sie / es ist wir sind ihr seid sie sind gelaufen gerannt geschwommen gesprungen

Now you might wonder how to know the perfect participle - we'll come to that just in a minute (chapter 15.3.2 to 15.3.5)

examples *   Ich habe einen Kuchen gegessen. = I have eaten a cake. Du hast einen Brief geschrieben. = You have written a letter. Ich bin nach Italien gegangen. = I have gone to Italy. Wir sind im See geschwommen. = We have swum in the lake.

* Don't mind quite yet about the position of the direct object in the sentence. The general rule is that the direct or the indirect object is right after the first conjugated verb (here habe). If there is a direct object as well as an indirect one, then the indirect goes first (again right after the conjugated verb), then comes the direct one and then comes the perfect participle. We'll have a look at them now.