The fastest way I can explain this is that the 1st ending “o” is always for when you’re talking about yourself (yo). The 2nd ending “as” or “es” is when you’re talking to someone else, referring to them as “you” (tú). The third ending “a” or “e” is when you’re talking about someone else using “he” or “she” (él/ella) or when you’re speaking to someone with a formal “you” (usted). The fourth ending is when you’re referring to “we” (nosotros). The fifth ending is for more than one person, “they” or “you all” (ellos/ellas/ustedes). Then lastly the 6th ending is for the other way of saying “you” (vosotros) which is not commonly used in the U.S.
sorry that this was long but I tried to be as clear as I could :)
