To summarize the argument:

• At first glance, the capitalist appears to fully compensate the wage-worker for their labor output, but if that were the case, the capitalist (on average) couldn’t make a profit! (Marx is working from what appears to be a Ricardian model which implicitly assumes perfectly competitive markets with long-run equilibrium commodity prices throughout this text, so the effects of oligopoly and imperialism on commodity prices aren’t considered). The reality is that the average capitalist is only required to pay a wage equal to a subsistence wage, the value corresponding to and which is needed to sustain an average worker’s labor-power (the term Marx uses in place of what bourgie economists might call human capital).

• Under a slave system, the kayfabe and reality are inverted: the slave doesn’t receive any explicit compensation for their labor from the master; but the reality is that the slave must implicitly receive compensation from the master, in the form of paying for the slave’s living costs.

• Feudalism by comparison is a more transparent and naked form of surplus-value extraction. There’s a clear and explicit spatial and temporal distinction between the labor-time a serf does on their own land to feed themself, and the labor-time done on the lord’s land whose fruits go to the lord.

• In all cases, the member of the exploited class renders a quantity of labor y=s+w, where s is the surplus gained by the exploiter and w is the exploited person’s compensation, bounded below by the minimum living cost/subsistence wage c. The capitalist pretends that the wage w equals the total output y (when in reality c<=w<y), claiming their profit comes from somewhere else; the slave’s master pretends that w=0 when w=c always holds; and the lord explicitly designates w and s separately.