The law allows a permanent resident to become a US citizen if it meets the following criteria:
What is the benefit of becoming a US citizen?
The benefits are many and it depends on your situation. Some of them are:
you can vote in local, state and federal elections
you can work for the Federal Government
you can travel and live in another country without the fear of losing your citizenship
if you like to travel, many countries do not require US citizens to obtain a visa
you can petition and bring your relatives (parents, husband, siblings, children, adult son/daughter) to live in the United States with an immigrant visa.
If you become a U.S. citizen while your children are under the age of 18 and meet other qualifications, your children may automatically become U.S. citizens as well.
How long does the process take?
It depends on what state you reside. In Nevada, the process takes about 3-4 months from the time you file your petition.
What is the US history and government test?
You will be asked to answer up to 10 of 100 questions you must study. In order to pass the exam you must answer at least 6 out of 10 questions correctly.
Here is a study guide for the test from USCIS