Hitler's initial idea for Poland was to annex the German areas and then set up a Polish rump state to govern the rest. He abandoned this idea in October of 1939 and instead deiced to use the General Government as "testing ground" to prove his racial theories. The German parts of Poland were annexed and either made into new provinces or amalgamated into older ones. Hitler set up the General Government to govern the area that wasn't annexed. It was under the authoritarian rule of Hanz Frank, a Nazi lawyer and minster of justice. The General Government was essentially a "colony" the Poles in the area were to be removed or killed and gradually replaced with German settlers. The idea of the General Government was that it would be outside the laws of the Third Reich, as Hitler put it, the General Government was to be the site of a:

hard ethnic struggle that will not permit any legal restrictions. The methods will not be compatible with our normal principals.

Hitler could not tolerate the Poles, and they were considered nothing more than pests who should be removed. The intention was to essentially prevent the Polish people or culture from reappearing. Again lets use Hitler's own words:

It was not the task of the administration to put the country on a sound basis economically and financially. There must be no opportunity for the Poles to reassert themselves. The standard of living in the country is to remain low; it is of use to us only as a reservoir of labour.

The General Government would have been annexed eventually, after the extermination of the Poles and the Germanization of the area had been completed. A similar policy was implemented in the East, with the Reichskommissariats.

Sources:

Third Reich Series by Richard Evans