There are overall four documents required for foreign tourists who want to travel freely in Tibet. One is the Chinese Visa, which you can apply for in Chinese Embassy in your country, one is Tibet Permit, which you have to obtain it in order to enter Tibet, one is the Travel Permit when you are planning to travel to the closed areas in Tibet which you can obtain it after you arrive in Tibet, and the other is the Military Permit, which you have to obtain if you are planning to travel to some military sensitive areas.