To answer this question, consider the monopoly of productive "tools and equipment." This monopoly, obtained by the class of industrial capitalists, allows this class in effect to charge workers a "fee" for the privilege of using the monopolised tools and equipment.
This occurs because property, in Proudhon words, "excommunicates" the working class. This means that private property creates a class of people who have no choice but to work for a boss in order to pay the landlord rent or buy the goods they, as a class, produce but do not own. The state enforces property rights in land, workplaces and so on, meaning that the owner can bar others from using them and enforce their rules on those they do let use "their" property. So the boss "gives you a job; that is, permission to work in the factory or mill which was not built by him but by other workers like yourself. And for that permission you help to support him for . . . as long as you work for him." [Alexander Berkman, What is Anarchism?, p. 14] This is called wage labour and is, for anarchists, the defining characteristic of capitalism.
This class of people who are dependent on wages to survive was sometimes called the "proletariat" by nineteenth century anarchists. Today most anarchists usually call it the "working class" as most workers in modern capitalist nations are wage workers rather than peasants or artisans (i.e. self-employed workers who are also exploited by the private property system, but in different ways). It should also be noted that property used in this way (i.e. to employ and exploit other people's labour) is also called "capital" by anarchists and other socialists. Thus, for anarchists, private property generates a class system, a regime in which the few, due to their ownership of wealth and the means of producing it, rule over the many who own very little (see section B.7 for more discussion of classes).
This ensures that the few can profit from the work of others:
"In the capitalist system the working man cannot [in general] work for himself . . . So . . . you must find an employer. You work for him . . . In the capitalist system the whole working class sells its labour power to the employing class. The workers build factories, make machinery and tools, and produce goods. The employers keep the factories, the machinery, the tools and the goods for themselves as their profit. The workers only get their wages . . . Though the workers, as a class, have built the factories, a slice of their daily labour is taken from them for the privilege of using those factories . . . Though the workers have made the tools and the machinery, another slice of their daily labour is taken from them for the privilege of using those tools and machinery . . .
"Can you guess now why the wisdom of Proudhon said that the possessions of the rich are stolen property? Stolen from the producer, the worker." [Berkman, Op. Cit., pp. 7-8]
Thus the daily theft/exploitation associated with capitalism is dependent on the distribution of wealth and private property (i.e. the initial theft of the means of life, the land, workplaces and housing by the owning class). Due to the dispossession of the vast majority of the population from the means of life, capitalists are in an ideal position to charge a "use-fee" for the capital they own, but neither produced nor use. Having little option, workers agree to contracts within which they forfeit their autonomy during work and the product of that work. This results in capitalists having access to a "commodity" (labour) that can potentially produce more value than it gets paid for in wages.
For this situation to arise, for wage labour to exist, workers must not own or control the means of production they use. As a consequence, are controlled by those who do own the means of production they use during work hours. As their labour is owned by their boss and as labour cannot be separated from the person who does it, the boss effectively owns the worker for the duration of the working day and, as a consequence, exploitation becomes possible. This is because during working hours, the owner can dictate (within certain limits determined by worker resistance and solidarity as well as objective conditions, such as the level of unemployment within an industry or country) the organisation, level, duration, conditions, pace and intensity of work, and so the amount of output (which the owner has sole rights over even though they did not produce it).
Thus the "fee" (or "surplus value") is created by owners paying workers less than the full value added by their labour to the products or services they create for the firm. The capitalist's profit is thus the difference between this "surplus value," created by and appropriated from labour, minus the firm's overhead and cost of raw materials (See also section C.2 — "Where do profits come from?").
So property is exploitative because it allows a surplus to be monopolised by the owners. Property creates hierarchical relationships within the workplace (the "tools and equipment monopoly" might better be called the "power monopoly") and as in any hierarchical system, those with the power use it to protect and further their own interests at the expense of others. Within the workplace there is resistance by workers to this oppression and exploitation, which the "hierarchical . . . relations of the capitalist enterprise are designed to resolve this conflict in favour of the representatives of capital." [William Lazonick, Op. Cit., p. 184]
Needless to say, the state is always on hand to protect the rights of property and management against the actions of the dispossessed. When it boils down to it, it is the existence of the state as protector of the "power monopoly" that allows it to exist at all.
So, capitalists are able to appropriate this surplus value from workers solely because they own the means of production, not because they earn it by doing productive work themselves. Of course some capitalists may also contribute to production, in which case they are in fairness entitled to the amount of value added to the firm's output by their own labour; but owners typically pay themselves much more than this, and are able to do so because the state guarantees them that right as property owners (which is unsurprising, as they alone have knowledge of the firms inputs and outputs and, like all people in unaccountable positions, abuse that power — which is partly why anarchists support direct democracy as the essential counterpart of free agreement, for no one in power can be trusted not to prefer their own interests over those subject to their decisions). And of course many capitalists hire managers to run their businesses for them, thus collecting income for doing nothing except owning.
Capitalists' profits, then, are a form of state-supported exploitation. This is equally true of the interest collected by bankers and rents collected by landlords. Without some form of state, these forms of exploitation would be impossible, as the monopolies on which they depend could not be maintained. For instance, in the absence of state troops and police, workers would simply take over and operate factories for themselves, thus preventing capitalists from appropriating an unjust share of the surplus they create.