How do I use "Essere" and "Avere" in the perfect tense?

First of all, in Italian the perfect tense has a precise structure:

-The auxiliary verb, essere or avere, in his present form (Io ho, tu sei, egli ha)

-The past participle, such as "mangiato" or "andato".

For example: Io ho mangiato ( I have eaten), Io sono andato ( I have gone), Io sono cresciuto ( I have grown up), Tu hai finito ( You have finished).

AVERE is used for all transitive verbs, even if it is used sometimes with other intransitive verbs ( e.g.: Camminare (to walk), Dormire (to sleep), Viaggiare (to travel).

ESSERE is used to express the "reflexive verbs", such as "Mi sono lavato" ( I washed myself).Furthermore, this auxiliary verb is also used for all verbs of movement and for verbs that express a change of state ( i.e. to grow up, to die).

However, there are a few exceptions where both are possible:  if the verb is indicating a change of state, you use Essere, if it indicates more of an action, use Avere. Some of this special verbs are cambiare, salire, scendere, aumentare, diminuire, finire, iniziare.