The future perfect tense relates action that, in the future, will be completed. Your T.A. asks you if you've done your assignment yet; you reply "Not yet, but by Friday I will have finished it". So, in English we capture both the futureness (will) and the perfectness (have).
To form the future perfect active indicative, find the perfect stem (3rd principle part less the final "i"), and add the personal endings.
Note: the personal endings are almost the same as the future of sum. (The 3rd plural future of sum is erunt; but the 3rd plural personal ending for the future perfect is, as below, -erint.) This might help you grasp the concept of the future perfect in Latin: for it entails both a perfectness (the stem), and a futureness (of sum).
To add: future perfect passive indicative; and maybe a note on why there is no future perfect subjunctive