How do you form the perfect tense using avoir?

The Perfect tense is formed of two parts -- the present tense of the auxillary verb (avoir or etre) + the past particple of the verb you are using!

Most verbs take avoir - to have, as the auxillary, but some take etre - to be.

The present tense of avoir:

J'ai

Tu as

On a

Nous avons 

Vous avez

Ils ont 

To form the past particple you take the stem of the verb and + the endings:

ER verbs = -er + é    parler -- parlé

IR verbs = -ir + i    choisir -- choisi

RE verbs = -re + u   vendre -- vendu 

Then you just add the two togther! 

ex.

J'ai choisi ! I chose 

Tu as parlé ! You spoke

There are some irregular verbs that take avoir as an auxillary - these you just have to memerise!