How do you form the perfect tense?

The perfect tense states that an event/action has been completed or is in the past: you have done something, something happened, you were in a particular state etc.

1. The majority of verbs are formed in the perfect tense using avoir as the auxiliary verb.

subject +avoir auxiliary + past participle

So take the appropriate for of avoir to agree with the subject of the verb:

j'ai, tu as, il/elle/on a, nous vons, vous avez, ils ont

Then to form the past participle of the main verb for different verbs:

-ER verbs: remove -ER and add é

-RE verbs: remove -RE and add u

-IR verbs:remove -IR and add i

So ...

I played cards: verb = jouer > J'ai joué aux cartes

I sold an icecream: verb = vendre > J'ai vendu une glace

I finished my homework: verb = finir > J'ai fini mes devoirs

2.  Verbs of movement and  state of being take être auxilliary verb. These verbs can be remembered by a simple mnemonic:

MRS VANDERTRAMP

Monter, Rentrer, Sortir, Venir, Aller, Naitre, Descendre, Entrer, Rester, Tomer, Retourner, Arriver, Mourir, Partir

subject + être auxiliary + past participle

So take the appropriate form of être: 

je suis, tu es, il est, nous sommes, vous êtes, ils sont

And for past participles as shown before! ( apart from naitre> né   and mourrir> mort)

Also, for être verbs, make sure you make the past participle agree with the subject. 

So...

Je suis arrivé(e) 

Tu es entré(e)

Il est descendu

Elle est venue

Nous sommes sorti(e)s

Vous êtes parti(e)(s)

Ils sont morts

Elles sont nées

Voilà!