The conclusion of an essay should include a restatement of your thesis and a brief explanation and leave the reader feeling convinced and satisfied. If Atticus is the character you most admire, then you will explain why in your thesis statement. Here is an example of a thesis statement.
Atticus is the character I admire most from To Kill a Mockingbird because he is willing to fight for what he believes in.
This is an example of the thesis you would have in the first paragraph of your essay. In that paragraph, you would preview your basic points, or reasons why you admire Atticus. In the conclusion, you review those same points. For example, you could explain that Atticus stands up to others in his town and is willing to defend a black man even when it is not popular. He also was willing to shoot the rabid dog to defend the town. These are the types of examples you can use.
You can also end with a quote. This is a meaningful way to leave your reader thinking. Find something Atticus said that you admire. For example, you might admire when he said this.
"Simply because we were licked a hundred years before we started is no reason for us not to try to win," Atticus said. (ch 9)
This quote is meaningful because it describes his fighting spirit, and why we admire Atticus.