When I was reading Silman's article http://www.chess.com/article/view/return-of-the-blunder-gland-part-two , and checking the position with help of a computer, I noticed that White's pawn capture on move 7 can make quite a difference. 

I can explain the position during an analysis , but I don't seem to have the awareness in a real game. A major issue in my play is to understand importance of pawn structure , and which piece to make capture when there are open options. 

The above diagram can arise from a French Defense. I have no idea about whether to take the pawn with Bishop or Knight. Can someone help me with this ?

Lastly , where can I learn more about a pawn structure ? It would be very helpful if you guys provide me a link or recommend a book title. I wish to improve under you help :D . 

For the last diagram, having reached something at least semi-similar in a simul against a WGM, I can say that in that case, taking with the Bishop was the right thing to do. (I took with the Knight and was absolutely slaughtered at about move 30)

Actually in the opening one may not provoke too many weakness for one capture , but maintaining a "healthy" pawn structure in middlegame seems elusive to me @@