Rammy. This game was typical of how a back three approach looks. But I understand that some people don't notice the same things on the pitch so it can look the same. I sit with my Dad and he says it always looks the same to him so there are always key moments where I point out the shape to him and how it differs. It is harder to do on a forum but I will attempt it anyway and maybe you can look out for it next time... Because it is written, though, I will have to generalise a bit.
So the 3 centre halves command the centre of defence, all generally playing within the width of the 18 yard box, even if one goes slightly ahead of the other two (which you will have seen in Derik being further forward as you mentioned), especially when we are in posession of the ball. However when the play switches and we are on the defensive the centre backs eventually drop into a stricter line (even though, depending on the play, the highest centre back may attempt to break up play or slow it down, which gives the wing backs time to recover into a defensive position, then Derik will drop into the centre back role fully.)
The wing backs have a licence to go forward, just like many full backs do - only as wing backs they can both go forward at the same time! Not just on the side we are attacking down. This gives us the "extra" man in midfield - and the mistake people make when thinking about an extra man is that they tend to look in the middle. This might seem confusing at first because if you drew a 3-5-2 formation on paper and compared the drawing to a 442 formation on paper - it would seem like the "extra man really is in the middle. So I will try to explain a little below.
Say the other team are attacking down the right wing, our defenders might drop into this formation...
So it could resemble a flat back 4.
...............................................................
..........CM...........CM........CM..........RWB
LWB.....CB........CB..........CB
................................GK
But if we win the ball back the LWB is now able to go forward with the rest of the midfield....
.................................CM...................RWB
....LWB.............CM.............CM
.................................................................
....................CB..............CB...........CB
......................................GK
or many variations of the above....
sometimes the formation is easy to confuse with other formations and can look like 442 or even a diamond at times, but the roles are different - the principle thing is not how it looks at any single moment in time it is more about the role assigned to each player and his movement or his instructions, and normally, you can see the layout aswell.
One final addition. Compare how the 3-5-2 looks when we have the ball (above) to how a 442 might look with a full back pushing forward.
................................CM..................RM
......................LM...............................RB
...........................................CM
......................LB........CB............CB
..............................GK
(Admittedly, hard to demonstrate what is in my head with dots and letters)