Usted is like - You, Sir. You, Ma'am. (formal and with respect for age/authority).
Ustedes is You (as in a group of people) formal but the only way to say this in Latin America. In Spain, this is considered you plural and formal.
Vosotros is like "you guys" "y'all", very colloquial, familiar, informal BUT for the most part used in Spain. This form is archaic in Latin America.
I hope this helps,
Best,