Answer to question 2 

White plays Bc4 and the black queen is pinned  as before.

At first it looks as if the black queen can capture the white bishop and that white will not be able to recapture.

Black has played Qxc4. 

 Now white can use his knight to fork the black king and queen. 

White plays Nd6+  and there is a fork.

 The knight is putting the black king in check and attacking black's queen at the same time. When the king moves out of check the white knight will capture the black queen.