The most famous aspects of the Treaty of Versailles, of course, are the so-called "war guilt" clause, the section establishing the League of Nations, and the other clauses that severely punished Germany for World War I and weakened that nation's military capability. These measures, of course, helped create a toxic atmosphere in Germany that could be exploited by radical groups like the Nazis.
The effects of the Treaty on the political geography, however, were also profound, and had major consequences in the coming decades. First, Germany had to return Alsace-Lorraine, the border territory seized as a result of the Franco-Prussian War in 1871, to France. Second, Germany saw the Rhineland, a territory lying between France and Germany that had previously been part of Germany, demilitarized, meaning the Germans could no longer occupy it militarily. Additonally, the coal-rich Saar Basin was temporarily occupied by the Allies. On Germany's Eastern frontier, the former empire had to cede large swaths of land to Poland, saw the former port of Danzig (Gdansk) declared a free city, and had to give up some land to newly-formed Czechoslovakia.
It should be noted that many of the most significant territorial changes associated with the Paris Peace Conference were the result of other, separate treaty agreements. These treaties saw the formation of several Eastern European nations out of the old Austro-Hungarian Empire, and represented perhaps the most dramatic territorial changes resulting from the First World War.