all levels of government in the us （federal（联邦）， state， and local） are elected by the people of the country.
federal government
the constitution of the us specifically limits the power of the federal （=national） government mainly to defence（国防）， foreign affairs， printing money， controlling trade and relations between the states， and protecting human rights. the federal government is make up of the congress（国会）， the president， and the supreme count（最高法院）。
congress
congress， the central law-making body in the us， is made up of the house of representatives and the senate. the house of representatives is the lower but more important of the two houses of congress. it has 435 members， called representatives or congressmen/congresswomen elected by their state. the member of representative（代表） for each state depends on the size of the population of the state， with each state having at least one representative. the senate is the higher but less powerful of the two houses of congress. it has 100 members， called senators（参议院）， elected by their state. each state has two senators.
congress decides whether a bill （suggested law） becomes law. if the senate and the house of representative both agree to a bill， the president is asked to agree.
the president can veto（=say no to） the bill（议案）， but congress can still make it a law if 2/3 of the members of each house agree to it.
state government
state government has the greatest influence in people‘s daily lives. each state has its own written constitution（宪法） （set of fixed law）， and among the state there are sometimes great differences in law on matters such as property， crime， health， and education. the highest elected official of each state is the governor. each state also has one or two elected lawmaking bodies （state legislature） whose members represent the various parts of the state.
local government
local government concerns laws made at the town， city or county level. these laws are usually limited to a small area and concern such thing as traffic， where and when alcoholic drinks can be sold， or keeping animals. the highest elected official of a town or city council.
every law at every level of government must be in agreement with（一致） the united states constitution. any citizen who thinks he or she has not been given their rights under the law may argue their case through all the courts up to the supreme court （the final court of appeal in the us） if necessary， and any law which is found not in agreement with the constitution （unconstitutional） cannot be kept in force.