some basic ideas on french defence

Further down is one of the key pawn structure that can occure on the french defence. 

the whites plans are:

1.take control of the e5 square and establish a knight there, moreover a bishop ore a rook would be also strong pieces on the e5.

2. pressure on the e6 pawn by doubling the rooks on the e file.

3. if the white player take control of the e5 square he can organize the game on the king site by gaining space with  f4 and possibly with h4-h5-h6

Blacks plans are:

1. Put pressure on the d4 square with c5-cxd4-.....Nc6 and sometimes Qb6

2. to put the bad bishop on c8 back to the game with Ad7-e8 and Bh5 or Bg6

3. to double the rooks on the F file and sometimes to sacrifice the rook on f3 (taking the whites knight) destroying the whites castle and removing a defender of the d4 square

4. to make with safe the e5 push and acquire a free, but also an isolated d5 pawn

Here is an illustrative game :