The governments derive their just powers from the consent of the governed. This can be seen in the Declaration of Independence, and it means that the people run the government.
In the Declaration of Independence, the people are given the right to run the government, not the other way around. The statement, "Governments are instituted among men, deriving their just powers from the consent of the governed" means that if a majority of the people do not like the government, they can change it. This form of government is very different from those governments run by kings and queens. If the people living in a monarchy do not like the way the government is being run, there is little they can do to instigate or bring about a change.
The idea of the people running the government was a new concept at the time when the Declaration of Independence was drafted. Even today, many countries do not enjoy the same freedom given to the people in the United States.
Countries such as Zimbabwe, Iran and Burma do not give people the freedom to make a change and often take away their rights if they try.
Elections are the primary way governments give power to the people. The presidential elections are held every 4 years and citizens can vote for congressmen every 2 years.