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,

Usted: second person singular. It is similar to "tu" but It's a polite form. For example, If you speak with an olf person use "usted"¿Necesita usted algo?. Ustedes: second person plural. It is similar to "vosotros" but It's a polite form. Same to before. You use "ustedes" to speak with old people, and You use "vosotros" to speak with a young people.