In order to enter the country permanently, you will need a valid passport and (depending on the country) an entry visa. Residence permits are issued by the official representation (embassy or consulate) of the country concerned in Switzerland. Generally speaking, retirees are required to demonstrate that they possess adequate financial resources as well as health insurance cover.
Thanks to the bilateral agreements between Switzerland and the EU, Swiss nationals are not treated as foreigners within the EU and EFTA. They can enter the member states with an identity card and register as permanent residents.