Classical Dutch
1) Look for videos on YouTube 2) Get a database and download a game collection of Classical Dutch games 3) Get The Killer Dutch Rebooted by Simon Williams 4) Study Simon Williams games 5) Start playing games and analyzing them after you are done.
Yes but 1) I can't find a useful classical dutch video at least for me 2) i dont have membership to analyse all my games
@1
Dutch is dubious and the Classical (e6 and d6) even more than the Stonewall (e6, d5, c6) or the Leningrad (g6).
The main idea is f5, Nf6, e6, Be7, O-O, d6, Nbd7, Qe8, Qh5.
The last time it was played in a World Championship Match was in 1935, by Alekhine:
https://www.chessgames.com/perl/chessgame?gid=1013159
https://www.chessgames.com/perl/chessgame?gid=1013180
@3
You can analyse your lost games without membership by invoking the engine clicking the icon bottom left.
Yes but 1) I can't find a useful classical dutch video at least for me 2) i dont have membership to analyse all my games
1) What videos have you watched and why aren't they useful to you? 2) You don't need a membership to analyze your games. Get yourself a database and get a chess engine. You can collect and analyze your games on that program.
I second post #2. I discovered the dutch by accident and then watched Simon Williams on youtube and got lots of great info! Its my favorite opening!

There is "The Aggressive Classical Dutch" by Nicholas Pert on chessbase.com. It's not free, but it's only 30 Euro.
I do not own that one, but have many of the others. Simon Williams did 2 on the English which I have. I have L'ami's on the Stonewall Dutch, Pelletier's on the Hedgehog, Trent's 60 minute one on the Ne2 Caro (That is the only 60-minute one I have - the 30 Euro ones are usually 6 to 11 hours of video content and then about 50 to 100 extra games beyond the ones covered in the video.)
I think Simon Williams also wrote a book on the Classical. Unsure, but I think it is called The Killer Dutch? I play the Stonewall, not the Classical, so not 100% positive.
Another thing to keep in mind. Neither the Stonewall nor the Classical should be played exclusively. They should only be played when White has played g3 by move 4. After something like 1.d4 f5 2.c4 Nf6 3.Nc3 e6, if 4.g3, only then should a Stonewall player play 4...d5 and a Classical player play 4...d6.
If White plays 4.Nf3, then Black should play 4.Bb4 now that Ne2 is not possible
If White plays say, 4.e3, then 4...b6! With pawns on e6 and f5, that Bishop wants to be on the long diagonal. That is the while point of 2.g3, 3.g3, or 4.g3 in the Dutch. To deny Black the ability to put the Bishop on the long diagonal. If White doesn't stop you from doing that, THAT should be your first priority after controlling e4 with f5, Nf6, and e6.

goal of classical dutch: control the lightsquares.
how black does that f5-Nf6-b6-Bb7 and even Qe7-Qg6
so white often chosses to fianchetto his bishop first
blacks goal is to fully control e4 and eventually acheive a kingside attack of some kind. Whites goal is to get e4 in before black can fully control it. Often times white is faster but black can get play with striking with e5 and attacking on the f file