An introduction to Shia Islam: Belief system, leadership and history

At this turn of the century, the terms Shia and Shia Islam are becoming increasingly known. What does Shia stand for? What is the difference between Shias and other Muslims? What is their perspective on humanity, the world, and other Muslims? What did occur by the time of Prophet Mohammad's death, and why did things turn out the way they did? Who was Imam Ali, and why do Shias consider him the successor of the Prophet? For what cause do they uphold mourning ceremonies? Who is it they mourn, and why? And why do they march out dressed in black? Who is Imam Mahdi, and why do they await him? Genuine questions asked by many, including Shias, but left unresolved. Is it not time to look for answers?