Tell me about the United Nations

The united Nations exercice a worldwide responsability and, yet, too often is little known by the general public. When and why was the United Nations founded ? What are its ideals, its goals and the means at its disposal for reaching them ? What is its structure ? How does it function ? What are the problems it faces day-to-day and in the long term ?
How can the men and women who head the organization and work for it, set aside the conflicts their own countries are involved in and devote their energies to the realization of mankind's loftiest goals: the establishment of a just and lasting peace for all in the world ?