Two chains meet in the middle of this position. White’s runs c3, d4, e5, each pawn defending the one in front. Black’s runs f7, e6, d5, doing the same job in the other direction.
The moves were 1.e4 e6 2.d4 d5 3.e5 c5 4.c3 Nc6 5.Nf3 Qb6, the Advance Variation of the French Defence, and every plan for the next twenty moves comes out of the shape those six pawns make.
8 
7 
2 
a b 
c 
d 
e f h 1 Attack the bottom, not the top
The pawn on e5 is the head of White’s chain. It is annoying, it takes the f6 square away from a black knight, and it is thoroughly defended. Attacking it head on with …f6 works only once the support underneath has gone.
So Black goes for the bottom of the chain instead. The moves …c5, …Nc6 and …Qb6 all hit d4, the link holding e5 up, and Nimzowitsch made this the rule in My System: attack a chain at its base, because that is the one pawn no other pawn defends. White does the mirror image on the other side, pushing f4 and then f5 at the e6 pawn that holds Black’s chain together.
Both sides are doing the same thing at opposite ends of the board. Whoever gets there first usually gets the better game.
The bishop nobody wants
Look at Black’s bishop on c8. Its own pawns sit on d5 and e6, both light squares, and they are not going anywhere. That bishop has almost no future until Black spends several moves rerouting it through d7 and b5, and it is the most famous bad piece in chess, the French light-squared bishop.
That is the standing cost of a chain: your pawns are all on one colour, so one of your bishops is permanently the worse one. Before you lock the centre, check which bishop you are locking in.
Space, and where to play
Whichever way a chain points is the side you play on. White’s pawns lean towards the kingside, so White attacks there with f4-f5, Nf3-g5 and a rook lift. Black’s lean towards the queenside, so Black plays …c5, …c4, …b5 and …b4 at the base on c3.
Get that backwards, and you are opening files towards your own king. If the idea of the chain deciding where the fighting happens is new, the page on the centre covers why d4, d5, e4 and e5 are the squares the chains are always arguing about, and pawn structure is the wider picture the chain sits inside.