Your claim (aka your thesis) is a one-sentence statement of what you will try to prove in your paper; it is likely the answer to the research question you developed earlier in the process. 

You will change your thesis as your ideas continue to develop- your teacher will ask you to draft a preliminary thesis and to continue to revise your claim based on their feedback. Don't expect to arrive at the "perfect" thesis on the first try, and keep in mind that it will take multiple attempts and perhaps more time than you expect to land on your final claim. 

Illustration by collayart via freepik.com