Unlike in English where 'you' is the only form to address a second person, in German you have three different words for it: Du, ihr and Sie.
Du – you (informal and singular form to address someone like a close friend, or family member)
ihr – you guys (plural form of 'du', when you address more than one person, like a group of people; it's still informal way)
Sie - when you address a respected person (formal), like your teacher or a stranger etc. Never mind, it's plural form is also 'Sie'.
Let's see few examples:
Kommst du heute Abend zu meiner Party? - Are you coming to my party tonight?
Kommst du aus Ägypten? - Do you come from Egypt?
Kommt ihr heute Abend alle zu meiner Party? - Are you guys (all) coming to my party tonight?
Kommt ihr aus Ägypten?- Do you (guys) come from Egypt?
Möchten Sie gerne eine Tasse Kaffee? - Would you like a cup of coffee?
Kommen Sie aus Ägypten? - Do you come from Egypt?
Look, in both examples (above) 'Sie' ist singular and formal. You are asking only one person. He or she is a respected one, may be a guest or stranger.
Now come on, let's say in a Supermarket you see a group of people speaking in arabic and you don't know exactly where they are from. You guess, they are from Egypt. So you ask them:
Kommen Sie aus Ägypten? - Do you come from Egypt? (look it's formal and you are addressing a group, plural)
By the way, when written with small 's', then 'sie' can stand for either 'she' or 'they'
Wer ist sie? - Who is she?
Sie ist meine Schwester - She is my sister
Wo wohnen deine Eltern? - Where do your parents live?
Sie wohnen in Berlin – They live in Berlin.