The Constitution is the framework designed to protect the People & their "natural rights" from the people we elect into power. It is to ensure that no one group or individual has a monopoly on the power delegated by the People. Thus, the Constitution is a contract between the People & those we elect and loan power to. They are there to protect our rights & their powers are limited by the brilliantly conceived document called the U.S. Constitution. It was intentionally designed to make government act in a slow & deliberative process. It did so by separating the powers of government into 3 branches: Executive, Legislative, & Judicial.
Declaration Of 
If the Constitution is the frame of silver then the Declaration of Independence is the picture of gold. Signed on July 4, 1776, it is unequivocally the fundamental motivation of how men were to be liberated from the heavy & cruel oppressive nature of governmental authority. It establishes that rights come from "Nature & Nature's God" and NOT from government & thus cannot be taken away by any moral authority. All governments must respect these rights & when they become hostile to them, the People have the right to alter or abolish such a government & create a new one respecting such Natural Rights.
Bill of Rights
The Bill of Rights was ratified on December 16, 1791, and is the first 10 amendments to the U.S. Constitution. It enumerates the fundamental & inalienable rights of man to Life, Liberty, property, and pursuit of Happiness, due process, and the limits of federal power. The Bill of Rights was a comprise of the Federalists to the anti-Federalist who clamored for it. The anti-Federalists would endorse the U.S. 
Constitution if and only if a Bill of Rights would be appended to the Constitution as law. This act of bipartisanship and cooperation ensured the ratification of both the Bill of Rights and the Constitution as well.