Generally people's "class" is defined by how much money they make. In the U.S. generally there are three classes: poor, middle class, and rich. Some people also think there is another class in between poor and middle class called working class. United States culture is based on the idea that people can move up the economic ladder and become middle class or even rich if they were born poor. This is the idea of going from "rags to riches". Moving up the class ladder is not easy though. Higher education needed to get a good paying job is expensive.
Class in the United States is more than just how much money a person makes though. Education, what job a person has, where they live, and the culture, all play a role in what class a person will be classified as. For example, a person with only a high school diploma and a low-paying service job may be considered poor or low class. While a person with a Ph.D., who owns their own company, would be considered high class or wealthy. In a way this makes sense because high-paying jobs usually require a high-level education. But for some people, class is something you are born with. For example, the children of billionaire Donald Trump were born rich and upper class without having done anything to earn that status.
Gender plays a role too in how someone can move up the economic ladder. Women earn less than men do, so it is harder for them to accumulate wealth. Race also plays a role in how much people earn and their ability to move up the economic ladder. In the United States, most families require both the man and woman to work in order to support the household.