8/8/4p3/4P2b/7N/8/5KPp/7k w - - 0 1
8.Nc1 and black is in zugzwang because he can no longer protect the g3 square appropriately, and must give up the h-pawn and the bishop for the knight.
Alena, a bit more convoluted than it needed to be, but you have the right elemental position between moves 10 and and 12. Of course, Dave had found the key element in his comment derived from one of your previous lines. The most concise route is the following:
It's a winning position for white.
Now think about this problem at this stage- white wants to bring the knight to g3 via e4, e2, f1, or h5. Black defends this by covering those squares with the bishop the move before the knight reaches them by staying on the h3/f5 diagonal. You will find that after move 5 (the previous moves in the line) that white can never accomplish this- the bishop has three safe squares on that diagonal, and always two safe moves while on it- that is too much flexibility for the knight to overcome to reach e2, e4, or f1. In addition, the knight can only reach h5 by coming from g3, which is irrelevant, and f6 and g7- but this also fails because black can always put the bishop on f3 safely since white can't let the black king off of h1 when the knight is on f6 or g7. This is why 1.g4 is an error- and that 1.g3 was the right start.
What you need to try to think of is a position where white can let the black king off of the h1 square safely- that is the type of position you are trying to create. What I notice about your problem solving is that you seem to always try a linear approach to them- you start of move 1 and try to work out where to go at each stage. This is perfectly fine a lot of the time, but you should always try to think about what a winning position might be- literally create one out of this problem, for example, then try to work towards that position from move 1.
Ok, I am going to show you a line that demonstrates the problem white has to overcome: