The UN?

I hear alot about the UN making descisions on a higher level than country leaders... i dont really understand how it works, How does the UN work, What is their purpose? Also if the UN can take measures to infiltrate countries with their armies... What countries make up the armies?

Is it right that there is a higher or World Government? Is there a top man(leader) of the UN?

Sorry for all the questions, and there probably stupid but i am not sure about the UN.

And3h

Don't feel stupid...the U.N. is anything but easy to understand. To me it is nothing more than a glorified debating society.

I believe, though, that it's origional intent was to be a sort of international watch dog.

Is there a Head Man?
Can so much responsabilty be given to one man?