There are two main types of international organizations. The first type consists of organizations that do not have governments or countries as members, and this type is called a non-governmental organization (NGO). The second type consists of organizations whose membership consists of countries, and this type is called an intergovernmental organization (IGO).
The first category, NGOs (non-governmental organizations) is very broad, and consists of any organization that has an international presence and does non-profit work. Organizations in this category can consist of everything from community oriented organizations to human rights organizations environmental organizations to religious organizations. Some examples are: Amnesty International, an organization that fights for human rights around the globe; Greenpeace, an organization that fights for environmental preservation internationally; the World Organization of the Scout Movement (WOSM), an international organization whose membership consists of national scouting organizations, such as the Girl Scouts of America (GSA) and the Boy Scouts of America (BSA), all educational and community-oriented organizations; Doctors Without Borders, an organization that provides emergency medical care all over the world; and the International Red Cross, a humanitarian organization that operates worldwide.
The second category, intergovernmental organizations (IGOs), consist of organizations that have representatives of individual countries' governments as members. The most well-known of these, the United Nations, is an enormous organization formed to foster cooperation between the countries of the world and enforce international law. The UN maintains international peace and security by sending peacekeeping forces to troubled areas; promotes sustainable development by fostering cooperation between countries to solve economic, political, social, cultural, and humanitarian issues; protects human rights via treaties such as the Universal Declaration of Human Rights; upholds international law via the international court at the Hague, the UN Security Council, and various treaties and tribunals; and delivers humanitarian aid in disaster areas. Other IGOs were founded to encourage cooperation between countries on issues of economic development and world trade. Some organizations that fall into this category are: the Organization for Economic Co-operation and Development (OECD), an organization that was formed to "promote policies that will improve the economic and social well-being of people around the world" (oecd.org/about); the World Trade Organization (WTO), an organization built to foster and regulate trade between countries; and several regional economic and trade organizations, such as the Association of Southeast Asian Nations (ASEAN), the Council of Europe, the African Union (AU), and the Organization of American States (OAS). All of these organizations foster trade and cooperation between their member states.