How does public opinion originate? Can it be manipulated?Public opinions impact policy making process.

I am assuming you mean history when you say "it."  I am basing this on the fact that you tagged this with "history making."  I am also basing it on the fact that you had it in the history section before someone moved it and edited the question.

History is, as Napoleon said, "a fable agreed to."  In other words, it is just a story that manages to get the most people to agree to it.  To me, competing visions of history are put forward by historians and journalists and such.  The ones that fit best with our ideas of what our past should be like, win.

Of course history can be manipulated.  We emphasize the things that fit with our vision of how the past should be.  We try to ignore those things that do not fit with our image.

Once we have a given history that we have agreed to, we often base public policies on it.  For example, since we in America believe that we came from independent pioneer types, we do not need a welfare state to take care of us -- we can do it ourselves.  Arguments based on the idea that we are self-sufficient do well in the US because of this view of our past.