The formula for this is M-C-M', or taking a sum of money M, turning it into commodities C, and selling C at its Value for a greater sum of money M'. This cycle repeats, and is only possible because the commodity "labor-power" is consistently purchased for well below its value, Capitalists pay the worker, say, 2 hours of work but expect 8-12 hours in return for said payment, and do so using the State apparatus to uphold this and prevent uprising against it.