There are three possible agreements this question might refer to. Abner Snopes comes to live and work on Major de Spain's property as a sharecropper. In exchange for the use of the house and the land on which to plant crops, Snopes must pay a share of whatever crops he raises to de Spain. Sharecroppers of that day typically lived a lifestyle barely better than slaves during the era of American slavery. Thus, Snopes refers to de Spain as "the man that aims to begin tomorrow owning me body and soul for the next eight months." This suggest that Snopes and de Spain have an agreement for a period of eight months that Snopes will work the land for de Spain and pay him a share of the harvest.

The next "agreement" Snopes and de Spain have is that Snopes must restore the rug he soiled to its condition before he damaged it. De Spain delivers the rug, but readers don't hear what he says. Snopes destroys the rug by adding a field stone to the water pot that contains the lye mixture the girls are using to clean the rug. Afterward the rug has permanent stains and the fibers are damaged.

De Spain comes to Snopes's cabin and informs him that he will charge him an extra 20 bushels of corn for damaging the rug. Snopes says nothing, but the following Saturday he appears with de Spain in front of the Justice of the Peace to sue his employer for demanding the payment. The Justice of the Peace rules in de Spain's favor, but realizing how even 20 bushels of corn will cause a financial hardship to Snopes and his family, he reduces the penalty to ten bushels. That is a legal sentence at this point, and Snopes must legally abide by that agreement.

However, Snopes evidently has no intention of keeping any of his agreements with de Spain. Instead, he sets de Spain's barn on fire, as he has done to others with whom he has disagreed.

In William Faulkner's "Barn Burning," Abner is supposed to farm the major's land and grow crops, then presumably give a set percentage of the proceeds to the major.  Abner and his family stay on the major's property and live in the shack provided for them. 

After Abner dirties the major's rug, he is supposed to clean it for the major, although this agreement is only inferred by the reader since we don't hear the conversation. 

Of course, before Abner can grow the crops, he ruins the rug by having his daughters clean it with lye, which destroys the rug.

Finally, the justice of the peace rules in the court case brought by Abner himself that Abner should pay the major ten bushels of corn to replace the ruined rug once the crop is harvested.  Instead, Abner decides to burn his barn.