The host opens the door and greets the guests. He welcomes them. At an official reception, this will be a formal affair. Guests line up to be greeted by the hosts:
Greeting your Wedding Guests: The Receiving Line | Bijou Wedding Venues
People exchange greetings, or greet people they know, simply to be friendly: For example, they say " Hello" to one another. I saw an acquaintance across the street and I greeted him with a cheery "Hello".