On examination of what White attacks you see his rook on the c-file aimed through the pawn on c6 and the queen behind it. The pawn is pinned—relatively—since it can't move without exposing the queen. The greatest value of pinning a pawn lies in your power to take something it protects. Here the pinned pawn protects the rook on b5, but the only piece White can use to take the rook is his own queen. Thus after the sequence 1. QxR, c6xQ; 2. RxQ, RxR, White hasn’t gained any material.
It would all be different, though, if Black’s queen were loose. The first thought thus might be to capture or drive away the rook on a8, but White has no way to achieve this. There is another way to loosen the queen, though: rather than driving its guard away from it, drive it away from its guard. Of course you need to keep Black’s queen on the c-file to preserve the pin you are trying to create, but if it could be drawn forward to c7, it would be loose and the pin would work fine. One way to attract a piece onto the square you want it is to put one of your own pieces there in a way that invites or requires its capture. The resource White can use for the purpose is his knight, via Nc7. Examine what threat the move would make and see that it forks Black’s rooks (as a color scan would have showed you anyway: the knight is on a light square, and so are both Black rooks). So Black might play QxN to avoid losing the exchange. Yet then he loses it anyway because now White can play QxR: if the pawn on c6 moves, White plays RxQ without worrying about a recapture.
In this case there already was a relative pin in place at the start, but it was weak. Since Black's queen had protection, and since White could only take advantage of the pin by throwing away his own queen, there was nothing to be made of it. Loosening Black's queen changed the profit structure of the pin, as it were, and made it much more powerful.
We have talked about three different ways of loosening a piece in the rear to create or improve a pin in front of it: capturing the rear piece and allowing a recapture by a piece that then is loose; going after the defender of the rear piece by taking something else it protects (attacking the defender directly is a possibility as well, of course); and drawing the piece away from its protector by putting a threatening piece en prise to it and attracting it forward on the line of the pin. Be mindful of all these techniques. They are useful methods for creating loose enemy pieces in many circumstances, as we have seen elsewhere; and loose pieces are your fondest sight as a tactician. They make a fine basis for a fork, a discovery, or a pin.