1. What a culture essentially is is rather hard to define. One view of it is that is is the collection of customs, beliefs, shared history, language and mutual feeling of belonging among a group of humans. Cultures are often a magnitude larger than countries, and may spread across continents.
A culture often contains numerous subcultures. Subcultures incorporate large parts of their mother cultures, but in specific instances they may differ radically. Some subcultures achieve such a status that they aquire a name of their own. A recent example of a subculture in the western world is punk.
Culture has nebulous bindings to the word civilization, and may in some contexts be roughtly the same.