what is the differance between 'Tu eres', 'Tu es', 'Usted eres', and 'Usted es'.
Well, for starters, "tú es" and "usted eres" are incorrect. Each pronoun has its own conjugation of any given verb, and they aren't interchangeable. It's like in English when you can say "I am" but not "you am". For the conjugation of the verb ser, this goes as follows:
yo-- soy (I am) tú-- eres (you are) él, ella, usted-- es (he/she/you formal is/are) nosotros/nosotras-- somos (we are) ellos/ellas, ustedes-- son (they, you plural are)
Do you already understand the difference between usted and tú? If not, this course has three different ways to say you in Spanish. For a friend, you use tú, which is informal. For people that you don't know or for those who are in a position of authority, you use usted (one person/singular), which is formal. For more than one person, use ustedes (plural) both formally and informally.
p.s. There are a couple other ways to say you in Spanish, but you don't need to worry about them unless you have friends in Spain or plan to go somewhere like Argentina.