In what ways are people's lives different depending on the social class in which they live?
People's lives differ depending on their social class because those in higher social classes have more money and more opportunities than those in lower classes. This is not to say that people in higher classes have no worries. However, their worries are of a different sort than those of the lower classes.
For example, let us look at issues of education. Middle class parents might worry about saving enough money to allow their children to go to a good state school (for college) without incurring too much student debt. By contrast, upper class parents might worry about getting their child into the right kindergarten (paying $10,000 a year or more) so they can get into the right private schools and so on up the ladder.
People in the upper classes in the United States live lives that are more materially opulent. They have opportunities (both in terms of economics and of recreation/leisure) that are not available to middle class Americans or lower.