What is the perfect tense and how do you form it?

The perfect tense in Spanish translates as 'to have done something' in English. It is used to express actions that begun in the past and are carried through to the present. For example, 'Todavía no ha traído los libros'/'She hasn't brought the books yet.' She did not bring the books in the past, and she still has not brought them in the present. It is also used for events which took place in the very recent past (usually that day). For example, 'Esta mañana no he desayunado'/'I didn't have breakfast this morning.' In this instance, the fact that I did not have breakfast this morning is still relevant to the present conversation, where presumably someone has asked me whether I did.This tense is formed using the auxiliary verb 'haber' (has) and the past participle of the verb (e.g. eaten). Haber is conjugated like this: he, has, ha, hemos, habéis, han. The past participle is formed differently for -ar, -er and -ir verbs. For -ar verbs we add -ado to the verb stem, for example, llamar--> llamado; for -er and -ir verbs we add -ido to the verb stem, for example, comer--> comido and dormir--> dormido. There are also some irregular past participles. Some of the most common ones are: abrir--> abierto, morir--> muerto, romper--> roto, escribir--> escrito, ver--> visto, and volver--> vuelto.