Socialism is a theory or system of social organization based on the holding of most property in common, with actual ownership ascribed to the workers.
Capitalism is a theory or system of social organization based around a free market and privatization in which ownership is ascribed to the individual persons.
Our current system of bad capitalism is ridden with widely deviating income classes and excessive unemployment. And under President Trump, it will only get worse.
Capitalism is not a political system. It is an economic system. Capitalism is not for everyday people who don't have millions of dollars. Capitalism is based on corporate interests. It is incredibly exploitative of everyday people for the benefit of a few. Under capitalism, you don't get out what you put in. The argument that if you work hard then you will succeed is no longer true for Americans today. Many people work full-time, have several jobs, and still can't afford to go to college, have health insurance, or adequately provide for their families. Capitalism has failed us.
In a socialist system, you get out what you put in. No one can exploit another person and take what they fairly earned. Socialism also encourages people to work together rather than against each other (which is a prevalent idea in capitalism).
Many people have skewed ideas of what socialism is thanks to a lot of the prominent figures in America. Socialism is not a system that fails to meet people's needs and controls their lives through a totalitarian government. (And yes, you still have private property.) It is a theory that believes that everyone should have access to public goods and basic articles of consumption. Socialists believe that the returns from large-scale industries must benefit a society as a whole.
Obviously, a capitalist society cannot become a socialist one overnight. And unfortunately, with our current president backtracking on all of Obama's moves towards redistribution policies, it will take even longer for socialists to dig their heels into our government.
Democratic Socialists of America: http://www.dsausa.org/
Socialist Party of America: https://www.socialistpartyusa.net/