Capitalism is a mode of production in which production is motivated by profit derived from the private ownership of the means of production. Those that own the means of production (factories, companies, etc.) perform no labour, but get paid from the difference between the value produced by those that do work and the value generated by that labour. This difference is called profit.

I own no significant means of production. The vast majority of my income comes from selling my labour power for a fraction of the value it generates. Thus I am working class, generating profits for capitalists.

Wealth and progress is generated by labour. I wouldn't have a good job and a computer if the forces of production hadn't been advanced so far. This advancement does happen under capitalism, but not exclusively. Worse, the mode of production can inhibit further advancement, like feudalism was inhibiting industrial advancement.

Capitalism fails all the time, it does it so often it's called the business cycle. Sometimes is fails catastrophically, like the Great Depression or 2008. It's being kept just barely functional by those that benefit from it; most of us don't.