The peace negotiations were after initial talks held in the cities of Münster and Osnabrück, an alternative favoured by Sweden (Hamburg and Cologne being the French alternatives). The two locations were needed as the Protestant and Catholic leaders refused to meet each other. The Treaty of the Pyrennes ending the war between France and Spain is also often considered part of the treaty.
The results of the treaty were wide ranging. Among other things, the Netherlands gained independence from Spain, and Sweden gained Pomerania, Wismar and Bremen-Verden. The power of the German Emperor was broken, and freedom of religion was imposed in the whole of Germany. Three new great powers arose from this peace: Sweden, the United Netherlands and France. Sweden's time as a great power was to be short lived, however.
The majority of the treaty can be attributed to the work of Cardinal Mazarin who was defacto leader of France at the time. France came out of the war in a far better poistion than any other power and was able to dictate much of the treaty.
It is often said that the Peace of Westphalia initiated the modern fashion of diplomacy as it marked the beginning of the modern system of nation-states. Subsequent wars were not about reasons of religion, but rather focused on reasons of state. This allowed Catholic and Protestant powers to ally, leading to a number of major reallignments.
Another important result of the treaty was it laid rest to the idea of the Holy Roman Empire having secular dominion over the entire Christian world. The nation-state would be the highest level of governement, subservient to no others.