With skewers as with pins, it sometimes happens that there are too many enemy pieces on a line: a skewer requires two of them, but instead there are three or four. The first important thing is to see these cases when they arise, and to notice the possible skewers despite the distracting extra men in the way. The second important thing is to know how to turn these situations into skewers that work. Again the techniques are familiar; only their application in this setting will be at all new.
Turning to the diagram, observe that Black has three pieces on the d-file. This suggests a possible pin or skewer, especially in view of a second point: White not only has a piece aimed through them on d1, but has two other pieces on the back rank; this is important because it means the piece on d1 is expendable. If it is sacrificed the rook on c1 can take its place in the manner we've seen in our earlier work with coordinated rooks. Thus White can simplify matters with a capture: he plays RxN and Black replies QxR. With this small and temporary sacrifice of the exchange White has created the kernel of a skewer; now with Rd1 he forces Black's queen out of the way, and once it moves it has no way to guard the rook. The d8 rook thus is left loose, so now White plays RxR+ and nets a piece—the knight he captured at the outset.