Use the Dutch as a surprize weapon as it is not quite sound and not played at top level chess.
The Dutch Defence is a closed chess opening. It starts with the moves:1.d4 f5
Stonewall Variation See above - Black should try to activate his dead bishop on c8 and play it to h5 and exchange it, or place it to b7 and then prepare the c-pawn push to c5. This set up is not very flexible for Black, but Black will not get overrun at the kingside because it is highly unlikely that White will be able to organize a kingside attack due to the blocked pawn structure f5,e6,d5.
Most popular in the beginning was the Stonewall variation (see above), but the Leningrad Dutch variation has become more popular nowadays where Black plays his bishop to g7. (called: Fianchetto)
Some top chess players have played it in earlier times like Alexander Alekhine, Bent Larsen and Paul Morphy. It was played in the 1951 championship match between Mikhail Botvinnik and David Bronstein.
However the Dutch is seldom played in top level chess nowadays as it is suspected to be not quite sound.
With the move f5 Black wants to control e4 to place a knight there later on in the game. This idea will be combined with an attack on the white king at the kingside. But this opening move weakens the black kingside and does not develop a piece. And it often leads to blocked and unflexible positions.
White tries to open up the center with e2-e4 or d4-d5 and combines this with an attack at the queenside.