What is a comparison essay and how do you write one?

I don’t have a clue as of what a comparison essay is and how to write one either. I have a 500-600 word essay to write in my US History class on foreign policies of McKinley, Theodore Roosevelt, Taft, and Wilson administrations and address the factors that influenced American foreign policy during the nineteenth and early twentieth centuries. I don’t know how to write a coparison essay or how to do an outline at all if anyone can help me i would really be happy. Please and Thank you. – Mrs. Richey

i think it is whenn u compare two tings