What would be done if you want to use these drives for separate purposes,
e. g. operating system on drive c: , documents on drive d: , etc.?

If you mean "splitting" a single drive into several partitions, you are talking about a term called Partitioning.

Well, this code would box the whole body of an html document. by using the relative value for position, you are telling it to position relative to its normal position, which the top left corner is at (0,0). by using left: 50px, you are telling the box to set the left margin  edge to 50px and by using top: 50px, you are telling it to set the top margin edge to 50px. by doing this shifting, the top left corner of the box, which is at (0,0) would be positioned at (50,50)