Sometimes you will find not one but two or three enemy pieces lined up on the same file or diagonal with their king. It may be that none of them can then be pinned, because a working pin (at least of the kind we now are examining) requires an unobstructed path from the king to the pinned piece and from the pinned piece to the pinning piece. How do you deal with excess enemy pieces on the needed line? There are a couple of standard ways. You might be able to threaten or lure one or more of them out of the way; or you might be able to capture one of the enemy pieces in a manner that requires the other enemy piece or the enemy king to recapture, thus simplifying the line and leaving the remaining piece pinned.
In this first example to the left, an inspection of Black’s king and its lines turns up two enemy pieces aligned with it: the knight and bishop on the d-file. Indeed, White’s rook on d1 already exerts the needed pressure for the pin; if either the bishop or knight were removed from the picture, the pin would be complete. This can be achieved by chasing one of the pieces away, and the best way to do this is with a pawn. Pieces flee pawns; they can't afford to be captured by them. So White plays c2-c4, and suppose Black moves his knight in reply. Now the bishop on d6 is left pinned. It has protection, so how should the pin be exploited? With another push of the same pawn: White plays c4-c5, and the bishop gets taken a move later.
When White initially moves his pawn to c4, it might have occurred to you that, instead of moving the knight on d5, Black can use his other knight to capture the pawn. Yes; but of course Black's other knight is then left loose, and White takes it with his rook. Still, that sequence does at least get Black a pawn in return for his lost piece.