So in fact there is "sie", "er" and "Sie". Both "sie" and "er" are written with a capital letter when at the beginning of a sentence which may lead to confusion when there is a "sie" with a capital "S". So "er" means "he" in English. The word "sie" can stand for "she" - so a single female person - or it can stand for "they". The word "Sie" is the polite form of "du" (singular person) or "ihr" (multiple persons) which in both cases means "you".