In formal language, affirmations have subject – verb – object complements order and yes/no questions have verb – subject – object complements order. So,
- Vous êtes beau is an affirmation.
- Êtes-vous beau ? is a yes/no question.
(If the subject is not already a pronoun, it comes first and a pronoun is added after the verb to form questions. E.g. Pierre est-il beau ?)
In casual language you'll find two more ways to ask a question:
Est-ce que vous êtes beau ?
Here, subject–verb inversion is limited (internal) to the universal “Est-ce que” question introducer.
Vous êtes beau ? …with the appropriate intonation.
In this case only the intonation (or the question mark in writing) allows one to understand it's a question.