Le Futur Antérieur

The future perfect tense – le futur antérieur – is formed as follows:

 –future tense of avoir or être (your helping verbs) 
-the past participle of a verb

  Avant minuit j’aurai fini mes devoirs, j’espère!
  Before midnight I will have finished my homework, I hope!

  Dans sept semaines, vous serez parties du dortoire 🙁
  In seven weeks, you will have left the dorm 🙁

About.com’s French Future Perfect explanation
    French Future Perfect formation

Use with  phrases such as QUAND, LORSQUE, DES QUE, AND AUSSITOT QUE:

(source) The future perfect is generally used to distinguish one future event that precedes another. It is frequently used with such conjunctions as quand, lorsque, dès que, and aussitôt que:

Ils auront déjà fini de manger quand nous arriverons. (They will already have finished eating by the time we get there.)

J’enverrai la lettre aussitôt que je l’aurai écrite. (I’ll send the letter just as soon as I have written it.)

*These sentences have a verb in the future, and a verb in the future anterior*

Tex’s French Grammar helpful site with listening