Money is, without question, the general equivalent. It is, as Uncle Karl indicated, the means by which we store labour. For my work I get money and I can use this money to instantly get the results of someone else's work. This is the genius of the capitalist. By creating money we are able to divide labour amongst ourselves and exchange it one with another.
The dark side of this, however, is that once we have an independent value for labour we find ourselves able to exchange any kind of labour for money. From building houses and sewing clothes through to building bombs and performing sexual acts. All of these things can be bought and sold at rates determined by the market. Each of them is a labour and each can then be given value.
And the means to produce this labour (and the products or services associated with them) can be owned, either by the individual or the collective. A building business owns the tools and buys the labour of the builders. A brothel owns the building and furnishings and buys the labour of the sex workers. The means of production is owned.
Money, as the general equivalent, can be used to regulate the exchange of material things. A number of bolts can be traded for some other number of cabbages through the equivalence of money. Cars can be exchanged for cattle. Cattle can be exchanged for other animals, and so forth. Interestingly, this allows for the exchange of the human animal for money. Slavery is well within the control of money. The physical material of a person can be exchanged for money. Money is not only the genius of the capitalist project, but it is also the exposure of that same project. A general equivalent is necessarily a universal equivalent. Any material, living or dead, can be exchanged for it. And people, being nothing more than living material, are part of that realm of the exchangeable.
Capitalism has brought us all kinds of interesting benefits, but it must be imprisoned and watched so that it doesn't get out of control.