Jak se jmenujete?
When to use
This is the standard, polite way to ask someone's name when you don't know them. It's appropriate for most situations when meeting new people.
Formality
This question uses the formal 'vy' (you) form, indicated by the verb ending '-te'. If you were speaking to a child or a close friend you already use 'ty' with, you would ask 'Jak se jmenuješ?'
Grammar structure
The phrase breaks down as: 'Jak' (How), 'se' (reflexive pronoun, part of the verb 'jmenovat se'), 'jmenujete' (you name yourselves - formal 'vy' form of 'jmenovat se'), and '?' (question mark). The verb 'jmenovat se' means 'to be called' or 'to be named'.
Notes
A polite way to ask for someone's name using the formal 'you'.