First, keep in mind that the resolution in a story line is the way in which the conflict (or main problem) is solved, or resolved. To Kill a Mockingbird is a long and complex novel. It has more than one main conflict. Therefore, there will be more than one resolution.
In order to answer this question, the next thing you need to consider is, "What are the conflicts which are resolved by the end of the story?" In this case, let's focus on two. The most obvious conflict driving the story is the Tom Robinson case, and Atticus' defense of a black man in a very prejudiced southern white town. This is a character versus character or character versus society conflict. In the conflict of Tom Robinson versus the town of Maycomb (or the jury, or Bob Ewell), the resolution is that Tom is found guilty of rape, and later killed while running from jail.
In the conflict of Atticus verus the town of Maycomb, the resolution is slightly more complex. Atticus chooses to defend Tom to the best of his ability and with complete honesty. It is obvious by the end of the trial, through Atticus' well presented case, that Tom Robinson is not guilty. When he is found guilty by the jury, Atticus is defeated in one sense. But in another sense, this conflict is resolved by the respect he gains from some of the people in town, and certainly from his own children. Atticus is able to hold his head high and know he did the right thing. His children are taught a valuable lesson through this conflict.
A second conflict presented in the story is the mystery of Boo Radley. In some ways, this is a character versus character conflict, and in some ways this is a character versus self conflict. Scout and Jem's fascination with Boo and who he is drives their childhood imaginations. However, by the end of the story, Boo becomes very real to them when he saves their lives from Bob Ewell. The mystery is resolved when Boo reveals himself fully to the children and allows Scout to walk him home on the final night in the book. For Scout, this resolution comes with her learning a sense of maturity, self-awareness, and acceptance of others who are different. For Boo Radley, who may have been experiencing a conflict of lonliness, this resolution confirms that he has a friend in the children he has been watching for so long from the shadows.