This sets up a potential pin on the d file which Black does not see.

Played to prevent Qxh7 when the Rh8 moves. Black would like to play the rook to one of the centre files.

This attacks the a7 pawn threatening mate in two and also pins the knight to the Queen.

The mate threat has been countered but at the cost of the knight. The extra centre pawn comes into its own.

Building up on the c file and attacking f6. c7 and f6 are pinned.

Threatens mate on c7 gaining a tempo to prevent Qxa2.

Every exchange increases the value of the extra piece, but here white also had to defend the a pawn. Black's Queen must stay in touch with the rook.

Advancing so as to create weaknesses or entry points by exchanging pawns near the Black's King.

Attempting to prevent b5 but...

he has missed that the c pawn is still pinned!