I would like to know after I got the schengen visa and If I have already starred the trip, Can I travel a country which has not include in the itinerary Within the trip. Thanks
A Schengen visa authorizes you to travel anywhere in the Schengen area, within the dates and length-of-stay restrictions printed on it.
If you go and do something wildly different from what you claimed in your visa application you wanted to do, and authorities find out about that, they might end up concluding that your visa application was a lie even when you filed it, and hit you with some consequences for lying on the application.
On the other hand, changes of plans are allowed. If you change your plans but you can (if challenged) convince the authorities that it's an honest change of plans that you didn't foresee when you applied, and which doesn't change the general purpose or character of your visit, then you have done nothing wrong.
It all depends on how good an explanation you have if you're challenged along the way; there are no bright lines to argue from. But it is rather unlikely that you will be challenged -- a random policeman doing spot checks will not have easy access to the particular details of your visa application.
Assuming you would visit another country in the Schengen zone, this is allowed with the Schengen visa.