How the videosystem works at different resolution?

Help to understand, please. On the screen color CRT the monitor with the maximal resolution, for example, 1024õ768 there are the physical pixels consisting of triads (1024 across, 768 on a vertical, all 1024õ768, the size of a pixel, for example 0,28 mm). At this resolution it is lit (whether or not) everyone physical pixel (elements of triads are lit whether or not everyone by the gun). And what occurs at resolution 800õ600? It turns out, that the "logic" pixels consisting from several physical are created. Not clearly only, how from 1024 pixel it is created 800, and from 768 - 600. Whether some are lit in part pixel or under any law it are passed? As occurs partial flash pixel (if it probably) and as this process is adjusted (the monitor or the videoadapter, in what their parameters). It would be desirable detailed explanations, and that can not understand in any way. Please, help to understand, or give the link to the literature.