In the United States, our democracy relies on three branches of government. These branches -- executive, legislative and judicial help to ensure that laws are fair and balanced. The system created by these three branches is called checks and balances. Here's a video that explains the idea of how the three branches balance one another.
Follow these links to find out more about the President (executive), Congress (legislative), and the U.S. Supreme Court (judicial.) Or learn more by playing a game on iCivics.org. Games like Branches of Power and Supreme Decision give you a look at some of the real-life issues faced by Congress, the President and the Supreme Court. (You can register for a free account or play as a guest.)
Here are some more places to explore for more information about the Federal government:
Ben's Guide to US Government for Kids has information for grades K-2, 3-5, 6-8 and 9-12.
Kids in the House is published by the Clerk's office of the US House of Representatives. This site has sections for Young Learners, Grade School, Middle School and High School.
For detailed information about state government in Oregon, the Oregon Blue Book is the go-to guide!