does anybody know how to actually follw through stonewall opening?

If you are trying to use it as a catch-all system against 1.d4, good luck.  It only works in certain circumstances:

1.d4 f5 2.g3

  After 2.c4 Nf6 3.Nc3 e6 4.Nf3, the move 4...d5 is horrible as it allows the ideal setup by White.  If White can still get his Bishops to f4 and d3 with no damage to his pawns, the system is a total failure for Black.  Here, 4...Bb4 is correct.

2...Nf6 3.Bg2 e6 4.c4 c6

Now 4...d5 is bad because White has not committed the King's Knight.  Here, 5.Nh3!! is very strong.  Black should always answer an early c4 move like this with 4...c6, allowing for the Classical setup after 5.Nh3.  For example, 5.Nh3 d6! playing for ...e5.

5.Nf3 d5

Now the Stonewall is fine

6.O-O Bd6 7.b3 Qe7

Against other move orders, it depends on White not being able to play Bf4 and Bd3 with the pawns undisturbed.

So the following is bad for Black:

1.d4 f5 2.Bf4 Nf6 3.e3 e6 4.Nf3 d5? because after 5.Bd3, White has the ideal setup.

But the following is fine:

1.d4 f5 2.g3 Nf6 3.Bg2 e6 4.Nf3 d5 5.c4 c6 6.O-O Bd6 7.Bf4

Because first off, the other Bishop is on g2, not d3, and after 7...Bxf4!, White's pawn structure is damaged after 8.gxf4.

You better learn the classical setup as well.

If you are implying playing the Stonewall Attack as White, DON'T!  It's no good because it requires commitment by Black to be any good, and with one less tempo of commitment by Black, black can take advantage.  Like if 1.f4, then don't play lines that allow a Stonewall setup by White to be any good, like go for the ideal Bishop setup, or don't play ...d5, etc.  If 1.d4 Nf6 2.e3?!, simply play 2...d5 3.f4? Bf5 intending 4...e6 and 5...Bd6.  Black is better.

So if you are talking White, find something else.  Black?  Make sure you have the Classical Dutch also in your arsenal and make sure you only play the Stonewall when White can't achieve the ideal setup (B on f4, B on d3, no pawn advance on the Kingside, such as g3).

What to do against 1.Nf3 as a Stonewall player?

In response to post 4 (rather than requoting the long post):

1.Nf3 - It often depends on what deviations you are willing to tolerate.  For example, after 1.Nf3 f5, White has the following deviations possible:

• He does not play d4, which means e4 is not weakened.  The reason why 1...d5, 1...Nf6, and 1...f5 are the most common moves against 1.d4 is because 1.d4 weakens the e4-square for White and these are the only three moves that control e4.  Well, with no d4 played, Black must always watch out for ideas with d3 and e4.  This is also true against the English Opening.  1.c4 f5 2.Nc3 Nf6 and then after something like 3.Nf3 or 3.g3 or other typical "English" moves, White still has the possibility of playing d3 and going for e4 himself, cracking the stonewall.  This does not make 1...f5 unplayable, but the theory is different!
• Watch out for Gambits, like 1.Nf3 f5 2.e4 (The Lisitsyn Gambit - Spelling?) fxe4 3.Ng5 and best here is actually 3...e5!, returning the pawn and then after 4.Nxe4, 4...d5!.  Black owns the center and will have easy development.

For all those interested in the Stonewall Dutch, I would highly recommend the excellent book "Win with the Stonewall Dutch" by Sverre Johnsen.  While the Stonewall is the bulk of the book (and the format is excellent, unlike any other opening book), he thoroughly goes through what to do against Gambit lines, lines where the stonewall is bad (i.e. Against London System players), move orders (like the answering c4 with ...c6, even if ...d5 is not played), and even a chapter on 1.c4 and 1.Nf3.  Highly Recommended!

I used to be a Dutch player (back around 2012 or so) and still play it occasionally, usually after 1.d4 e6 2.Nf3 I sometimes play 2...d5 and other times play 2...f5 since he doesn't have the Nh3 lines any more, and after 1.d4 e6 2.Nf3 f5 3.c4 e6 4.Nc3, you have the 4...Bb4 line mentioned above, and this is pretty much an "Accelerated Nimzo-Indian" by Black, and low and behold, my main repertoire is what?  1.d4 e6 2.c4 Nf6 3.Nc3 Bb4.  And in the Nimzo-Indian, there is a line known as the "Dutch Variation", which I believe is 4.e3 b6 followed by I think Bb7, Ne4, and f5 - might have left a move out - been a while since I played it as late I have answered 4.e3 with 4...c5, but still, the variation exists!)

So long story short, there are answers to 1.Nf3 where you may be able to play similar lines, and sometimes it might directly transpose, but don't expect there to be a simple "systemmatic" answer to it!

sounds very interesting. teach me as well

Already gave it to you - Invest in the book mentioned in post 7.  You can order it from Amazon or many specialty sites that sell chess books and equipment, like Chess 4 Less, USCF Sales, or the London Chess and Bridge center site.