How many days of "Creation" where there? If the answer is 7, then why is shabbos considered a day of Creation?
The days of B'raishis are referred to commonly by Hazal as Sheishes Yimei B'raishis. However it does say "Vayichal Elokim BaYom HaShvi'i which means the Almighty finished on the 7th day. Rashi is bothered by the fact that the verse said right after Yom Hashishi that "The heavens and Earth and all their hosts were completed". Did Hashem finish on the 7th or the 6th? He answers that Shabbos brought the concept of Minuha, rest to the world. Without the concept of rest the world was not yet complete. The concept of rest means to stop creating. So by stopping, Hashem completed creation. Avin Ezrah (yes, that is how it is pronounced! see http://onthemainline.blogspot.com/2010/01/how-should-we-pronounce-ibn-as-in-ibn.html) says that Hashem resting means He set the laws of nature as constant. It is all there in your Mikraos Gedolos Humash.
shabbos is the creation of rest. hashem is teaching us that even he, who created the world, took a day to rest, and so should we.