How we cite our quotes: (Chapter.Section.Paragraph) or (Chapter.Paragraph)
Quote #1
The wealth of societies in which the capitalist mode of production prevails appears as an 'immense collection of commodities'; the individual commodity appears as its elementary form. Our investigation therefore begins with the analysis of the commodity. (1.1.1)
In this opening passage, Marx says he'll start his analysis by looking at the commodity, since that's what makes up wealth under capitalism. Perhaps he was inspired to start this way because one of the earliest and most important major works of economics was Adam Smith's Inquiry into the Nature and Causes of the Wealth of Nations, which announces in its title the same concern: the wealth of the world.
Quote #2
Socially necessary labour-time is the labour-time required to produce any use-value under the conditions of production normal for a given society and with the average degree of skill and intensity of labor prevalent in that society. [...] What exclusively determines the magnitude of the value of any article is therefore the amount of labour socially necessary, or the labour-time socially necessary for its production. (1.1.15-16)
This is Marx's fundamental concept of value: socially necessary labor time. While wealth is made up of commodities, the value underlying them is made up of labor-time. In other words, the socially necessary quantity of time that goes into producing a good or service is what constitutes its value. The socially necessary part means that when you calculate the value of a commodity, you consider the average (that's the socially part) amount of time required (that's the necessary part) to produce it, not some unusual scenario where a worker is taking a million years to make the item.
Quote #3
The mysterious character of the commodity-form consists therefore simply in the fact that the commodity reflects the social characteristics of men's own labour as objective characteristics of the products of labour themselves, as the socio-natural properties of these things. Hence it also reflects the social relation of the producers to the sum total of labour as a social relation between objects, a relation which exists apart from and outside the producers. Through this substitution, the products of labour become commodities, sensuous things what are at the same time supra-sensible or social. (1.4.4)
This is Marx's famous concept of commodity fetishism. An object is really just an object, but once that object is for sale, we see it as having a lot of extra meaning, just as people see a fetishized thing as having sexual meaning that the thing itself doesn't ordinarily have. The extra meaning of a fetishized commodity is that its exchange-value represents the amount of labor-time people worked to create it. Wealth under capitalism, then, creates magic-seeming objects, commodities.
Quote #4
The first distinction between money as money and money as capital is nothing more than a difference in their form of circulation. The direct form of the circulation of commodities is C-M-C, the transformation of commodities into money and the re-conversion of money into commodities: selling in order to buy. But alongside this form we find another form, which is quite distinct from the first: M-C-M, the transformation of money into commodities, and the re-conversion of commodities into money: buying in order to sell. Money which describes the latter course in its movement is transformed into capital, becomes capital, and, from the point of view of its function, already is capital. (4.4)
Selling in order to buy (C-M-C) and buying in order to sell (M-C-M) are the two fundamental processes of market exchange. It's what we do with wealth, our commodities. Capital is the latter process. That means Marx doesn't picture capital as an unchanging thing, but instead as something in motion, a type of circulation of commodities.
Quote #5
The process M-C-M does not therefore owe its content to any qualitative difference between its extremes, for they are both money, but solely to quantitative changes. More money is finally withdrawn from circulation than was thrown into it at the beginning. The cotton originally bought for £100 is for example re-sold at £100+£10, i.e. £110. The complete form of this process is therefore M-C-M', where M' = M + ΔM, i.e. the original sum advanced plus an increment. This increment or excess over the original value I call 'surplus-value'. (4.15)
There's no reason to buy in order to sell (M-C-M) unless you think you're going to come out of the process with more money. The more money you end up with if you successfully buy in order to sell at a higher price is called surplus-value by Marx. Think of surplus as meaning extra, like the extra items that make up the stock at a surplus store.
Quote #6
The simple circulation of commodities—selling in order to buy—is a means to a final goal which lies outside circulation, namely the appropriation of use-values, the satisfaction of needs. As against this, the circulation of money as capital is an end in itself, for the valorization of value takes place only within this constantly renewed movement. The movement of capital is therefore limitless. (4.17)
Selling in order to buy means you wind up with a use-value, which you then consume, such that the commodity leaves the market exchange system (the sphere of circulation). But buying in order to sell keeps the commodities in circulation; the process keeps going and going. That's why capital (the process of buying in order to sell) can keep seeking surplus-value forever, at least as long as the market and the commodities continue to exist.
Quote #7
In order to extract value out of the consumption of a commodity, our friend the money-owner must be lucky enough to find within the sphere of circulation, on the market, a commodity whose use-value possesses the peculiar property of being a source of value, whose actual consumption is therefore an objectification of labour, hence a creation of value. The possessor of money does find such a special commodity on the market: the capacity for labour, in other words labour-power. (6.1)
How can capitalists make more money when they sell in order to buy if all commodities are exchanged at their value? Marx's project in Das Kapital is to describe an ideal capitalism where commodities are traded for what they're worth. So where does the surplus-value enter the system since all the traders know the scores? Well, there is one special commodity, Marx says, which can create value. That is labor-power.
Quote #8
Given the existence of the individual, the production of labour-power consists in his production of himself or his maintenance. (6.11)
The capacity to labor (labor-power) is primarily used in keeping the individual worker who possesses it alive. This is the necessary labor that must be done in all societies, capitalist or not.
Quote #9
Our capitalist stares in astonishment. The value of the product is equal to the value of the capital advanced. The value advanced has not been valorized, no surplus-value has been created, and consequently money has not been transformed into capital. (7.2.19)
Marx has just finished describing how no surplus-value is created by laborers simply making products during the portion of their working day that constitutes their value—the part that takes care of the cost to keep them alive. Picture a simple tribe gathering berries and eating them. There's no profit, even though they might have instruments of labor (tools) to assist them. So where does the capitalists' surplus-value come from? See the next quotation.
Quote #10
The fact that half a day's labour is necessary to keep the worker alive during 24 hours does not in any way prevent him from working a whole day. Therefore the value of labour-power, and the value which that labour-power valorizes in the labour-process, are two entirely different magnitudes; and this difference was what the capitalist had in mind when he was purchasing the labour-power [...] What was really decisive for him was the specific use-value which this commodity possesses of being a source not only of value, but of more value than it has itself. (7.2.22)
This is the trick of capitalism, according to Marx. Workers might need to work only half a workday to produce enough value to support themselves. But that doesn't prevent capitalists from requiring them to labor the entire workday to receive any wages at all. There's all this surplus or unnecessary labor being done to produce surplus-value. Workers try to shorten the workday through class struggle, but as long as capitalism exists, capitalists have to find surplus-value and so will continue to exploit workers, or make them labor more than is required for them to sustain themselves at a given standard of living.