Okay, so Das Kapital means "Capital" in German—you probably already figured that out. The point of the title is that Marx is analyzing capitalism, and the main motor of that economic system is—you guessed it—capital. Capital is the M-C-M' process, "the transformation of money into commodities, and the re-conversion of commodities into [more] 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).
A few points can be made about this. First, capital is an impersonal force. It's just money making more money. Whether an individual capitalist is a good person or not isn't Marx's focus; in fact, he says that competition forces all capitalists to be ruthless, since if they're not, their competitors will put them out of business.
Second, capital steers capitalism. Without capital seeking to valorize itself, as Marx puts it (valorization means the adding of more value), capitalism doesn't go anywhere.
Finally, Marx is analyzing an ideal capitalism, one that's functioning according to the depiction of his opponent economists such as Adam Smith and David Ricardo. That means Marx isn't considering abnormal circumstances, such as, for example, commodities selling at prices other than their fair price (see 10.1.1. for instance).
Das all there is to it!