Your thesis statement is the main idea of the essay.
You place the thesis statement at the end of the introduction paragraph.
Your thesis will vary according to the topic of your essay, but some general characteristics of the thesis statement are:
(1) one sentence
(2) not a fact
(3) an opinion or claim about the specific topic
(4) the claim requires supporting evidence
As in (3) above, the specific topic must be the focus of your claim. So if you choose to write an analysis of a character, your thesis statement must make a claim about that person. What kind of person is he / she? What is important or special about the character in the novel?
See the model essay for further details.