Ok, here is one of those games which I felt I lost on impulse.. by making one stupid move.

What I want to knew, apart from two obviosu stupid moves... where did I slipped off, and how could I have forced a win, when I think, I have an upper hand.

Bf4??

Bg5!

Seems like your move on 19 was bcause you didn't have a plan.   An eagerness by me to grab a free pawn has often been my undoing.

Push the Efile pawn up to fork the and D pawn.  Looks to me black has to make a choice to either degrade the kings defenses or move A file rook into defense.   That makes the A&C pawns a much greater threat to promote.

 Hm.. yes, lack of planning has prompted the blunders.  Thanks, e-pawn promotion sounds good, I do beelive that I did have peices to carry out atack on central king, if needed.

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You seem to be deriding many of your own moves (for example, the "stupid" 17 Nxd5 was perfectly fine, and 17 cd would've lost a piece to 17... Ba6), but by the 18th move you've built up an overwhelming position.  I think 19 c5 was very strong...if then 19... bc 20 Ng5, the idea being that 20... Nxg5 21 Rxb8 wins the queen (21... Qxb8 22 Qg8+).  Also if 20... d6 21 Bb5+ induces mayhem.

For that matter, even on your 21st move (when you're already a rook down) 21 Ng5 still unleashes some formidable threats.  After 21... d6 22 c5 can follow.  Black's scattered pieces are not well-disposed to cope with the onslaught from White's aggressively posted forces.

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Hm... These are quality moves. I wil keep them in mind, not that this pattenre occurs many times. But it did have good touch.

Bg5! Well, I think game would have gone:

7 .. Ke6 8. d5 (trying to exploit the centre wekaness of black) Nf6

Bg5 seems excellent move, but I cant find any way to exploit it. Can anyone tell em how to?

Yea, your "free pawn" cost a rook, and THEN you went on to trade down.  Just look before you leap, my best advice.