The United Nations play a very important role in maintaining peace and security in the present times. Moreover, its specialised agencies are the pillars of modern world. Agencies like the WHO, UNICEF and FAO have done significant work in providing food and medicines in developing and underdeveloped countries.
However it also to be noticed that the UNO is dominated mainly by Western countries. Its rules and policies are framed by developed countries. Moreover, the Security Council which takes imporant decisions on world affairs is dominated by five countries- the USA, China, France, Britain and Russia. THese countries put their own interests first while taking any decisions.
So, the relevance of the UNO is that its agencies are playing an important role. But its five permanent members are driving the world politics to suit their own interests.