what is the purpose of our U.S. government?

Answer 1

In a very short answer:
The government's role is to PROTECT the Life, Liberty, and the Pursuit of happiness of the people it SERVES.

Answer 2

Your best bet is the Preamble of the Constitution.

"We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defense, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity, do ordain and establish this Constitution for the United States of America. "

Added here is some analysis from findlaw.com...


[Annotations
PURPOSE AND EFFECT OF THE PREAMBLE

Although the preamble is not a source of power for any department of the Federal Government, 1 the Supreme Court has often referred to it as evidence of the origin, scope, and purpose of the Constitution. 2 ''Its true office,'' wrote Joseph Story in his COMMENTARIES, ''is to expound the nature and extent and application of the powers actually conferred by the Constitution, and not substantively to create them. For example, the preamble declares one object to be, 'to provide for the common defense.' No one can doubt that this does not enlarge the powers of Congress to pass any measures which they deem useful for the common defence. But suppose the terms of a given power admit of two constructions, the one more restrictive, the other more liberal, and each of them is consistent with the words, but is, and ought to be, governed by the intent of the power; if one could promote and the other defeat the common defence, ought not the former, upon the soundest principles of interpretation, to be adopted?'']

Answer 3

To dig holes and sell shoes.
Everybody knows that.
There is a rumor that our government is supposed to promote and support the general welfare of it's citizens by providing and administering a level of civic reponsibility.
But that's a load of crap.
The real purpose is to dig holes and sell shoes.

Answer 4

You need to do some reading. Here. http://www.constitution.org/constit_.htm