I have a question in this position
With correct play white should win this position, let's not forget black king is still in middle and white is not just gonna sit there and applaud blacks' wonderful plan. black is behind in development.
That is a seriously good question. I often find writers of books make statements based on the assumption that the reader is on some wavelength when he's really somewhere else.
Statements like that need more clarification.
I think best black move in the position is E5. we put bishop on E5 if white exchange it, than as soon as possible do 0-0. and trying to exchange centers pawn and take control of center field
Just to explain each of the moves: d6 takes control of the e5 square. After that nf6 prepares the castle. The idea of playing b5 and b4, is to increase the strength of blacks strong dark square bishop on the long diagonal. Currently the b2 and c3 pawns limit it's potential. by playing b4 and forcing white to do something with c3, the bishop will become stronger on the long diagonal.
Also, proplylaxis moves can be very important, but before you play those kind of moves be sure if the thing you are trying to prevent is actually a real threat.
Read it carefully, it says a defensive state where you react to threats. Prophylaxis is not reacting to threats (but merely bringing your pieces into contact with strategically important points).
Like tonydal says, if you're worse you have to react, but of course you never want to aim for this. Beginners though have a very weak will, and often react to the smallest threats, and many times threats that aren't even there -- Silman's advice is common and sensible enough for sure.
Complicating your opponent's most natural play I suppose could be thought of as reacting to threats, but this is very different than the kinds of threats he's talking about.
The b5-b4 advance, as he says, opens more fully the line of the black bishop. It seems Silman says to seek play on the queenside. I guess with no targets for white and active minor pieces for black, the queen will be clearly worse? That's what it seems like he's saying anyway.