Capitalism is an economic and political system in which a country's trade and industry are controlled by private owners for profit1.
It's a system that's run by and incentivizes greed, that has created a huge wealth disparity between the mega-rich that own most of the means of production and the workers who staff their factories and businesses.
There is huge waste of resources and serious threats to mankind in the rivalry and arms race between imperialist and social-imperialist powers. There is cutthroat competition among the capitalist countries, while third world countries and people demand emancipation and development. All these are putting every capitalist country in dire straits.
Workers under capitalism are directly hurt by the owner's goal to maximize profit. To make more money, the owner want to cut down on as many costs as possible - which often means the worker's wages. If wages rise too high, owners will outsource the production to poorer parts of the world where labor is cheaper in order to save money.
Capitalism moves into every area of work and community, harnessing all of social life to its pursuit of profit. It converts nature, labor, science, art, music and medicine into commodities, and commodities into capital. It transforms land into real estate, folk culture into mass culture, and citizens into debt ridden workers and consumers.
Often, workers become discouraged and exhausted dedicating such a huge portion of their lives to doing work that ultimately benefits somebody else. They experience alienation and depression as a result. The metric with which capitalism judges the health and ability of its citizens is ability to work, as seen in the legal definition of "disabled".
Private profit gained by capitalists becomes frozen in unproductive assets or wasted on luxurious, conspicuous spending by a few. It contributes to unnecessary and bloated costs of administration, like excessive salaries, allowances and bonuses for the bosses and the high, unnecessary costs of private economic competition and bankruptcies.
Most crimes and legal cases today relate to capitalism because they relate to private property and poverty.
To understand capitalism, one first has to strip away the appearances presented by its ideology. Capital annexes living labor in order to accumulate more capital. The ultimate purpose of work is not to perform services for consumers, or sustain life in society, but to make more and more money for the investor, irrespective of the human and environmental costs.
To better understand capitalism, we must also understand its opposite: socialism.
Also check out Marx's criticisms of Capitalism