This is a question to all Americans. Can you explain the N word?

I am English, and consequently have no understanding of this at all. Also, why do you think your country contains so many racists in general? I am a minority, I won't say which one, and the Americans that I have met seem very aware and conscious of this fact, as though they are subconsciously trying very hard to ignore the fact that I am different, rather than accept that it is a part of who I am. These people, ironically would consider themselves liberals.