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.