Green Card
To move to another country, you will need a so called “Green Card”. You can apply for this if you are going to study or work abroad. The Green Card is a must for a foreign citizen to live in another country´s territory. In some countries they use a visa which means you are permitted to travel into the country and stay for a specific time. If you don´t have a Visa or Green Card you can be rejected to enter the country and immediately sent home to your country, where you have your citizenship. A Green card, or a Visa can be revoked if you for example commit a crime in the country where you have the Visa.
Free movement
There are people who have what is called Free movement. They don´t need a Visa or Green Card. For example, citizens of the Nordic countries, Sweden, Norway, Finland and Denmark, have the right to visit and stay in the other Nordic countries whenever and for as long they wish. The same applies to the Benelux-countries, citizens of Belgium, Netherlands and Luxemburg, have the right to travel and stay in the countries as they wish. Besides this, citizens of all EU countries have the right to travel and move to other countries in the union provided that they can provide for themselves and family if they come along.
Different kinds of permits
There are different kinds of permits, they differ in the way that some are permanent while others are temporary. The permanent one is for all time but can be revoked in special cases like for example repeated criminality. The temporary one is valid for a limited time and can, sometimes, be extended for special reasons. An example can be a worker at a multinational company with a four-year contract for duty in a country, and the contract gets extended to six years. In such a case, the employee or the company can apply for the extension for special reasons. A residence permit can also be given in special cases, for example those seeking asylum, if there is a threat in their own country or if relatives have moved to the country where they are seeking asylum.
The Green Card-system
The system with a Green Card was developed by the USA and has been applied in many countries. It gives foreign citizens the right to work in the country, The Green Card is a permanent residence permit as well as a worker permit often preceded by a temporary Visa or permit. A Green Card is often the beginning to the process of immigrating and getting a new citizenship.
Points system in the United Kingdom

The United Kingdom practice a system with points, much like the Green Card system in the US and Denmark. An immigrant needs a certain amount of points to get a permit. The count is based on education, age, earlier employment and salary, estimated salary in Great Britain. Other factors, also affecting the point count, is language knowledge, capital and qualifications. To immigrate as a worker to the United Kingdom the points required are different depending on what kind of work you are going to have. Category One is the highest qualifying and includes those with an exam from British universities, investors and entrepreneurs. This category is most likely to get a permit. Category Two includes qualified workers with a work offer. Category three includes lower rated professions where there is a lack of competence. Category four is for students and Category five for temporary labour and youth, like for example au pairs.
To get answers to any questions you can easily contact the country in question or the embassy where they can help you with everything you need to know.