Satellite Radio?

Does Sirius and XM radio work in Canada and Alaska? Does it work all over the globe including Australia and Western Europe? How does it work? What does the satellite in space look like? Is there more than one Satellite? Is there a Satellite for every channel? What are the odds of the Satellite getting knocked out of orbit? How does the technology work exactly? And why do Trees buildings and freeway overpes block out my reception sometimes?