Defending after losing possession

I was recently told by one of my teammates that I was not dropping down to defend when we lost the ball. I wasn't sure of where exactly I was supposed to drop down. So I asked him and he answered my question.

I knew that I had to be in line with my attacking midfielders, but I was standing too much to the opposite flank of where the ball is. I don't need to stand there because there's no need to mark anyone that side, only once the ball is switched I press the full back next to me. I need to come inside towards the center of the field. When I come inside I let my attacking mids to block passes on the other flank. I have to take their role of the central area. 

To visualize this he said this. We play a 433, when we lose the ball we change to a 451. The midfield changes to a 5 because both the winger tuck in and make it harder for the opponents to get past our lines. 

That's it