The Ten Commandments was a bullet-point summary of one of |God's early speeches (back when he had better speechwriters) carved into solid rock via cartoon laser beam in 1956 for only Charlton Heston to witness.  It was a monumental code of basic law and morality for all people to follow, and served this purpose for all of five minutes before
Chuck Moses shattered them on a big statue. Oops.
God used a primitive version of Microsoft PowerPoint to compile the list, as he knew Chuck was a visual learner with a short attention span. In addition to taking a granite-template background and serif-script Hebrew font, he used a flashy horizontal fire-wipe ingress for each line. This was not then standard in MS software, but God was a skilled programmer and graphic designer, so he had it up an running in no time, thoroughly impressing Elohim at the last staff meeting.
The Ten Commandments are the inspiration for every legal and moral system ever to exist for mankind, since before the imperialism and globalization of Christianized Western culture in the late 19th Century to mid 20th Century. At least that's what Christian fundamentalists like to imagine, people kinda just dicked around and stuff. In fact, they inspired people who didn't even know about them, like U.S. Representative Lynn Westmoreland (R-GA), who didn't even really get the gist of the Commandments yet still knew that they were important enough to be put on all government buildings. 
Actually human societies got on OK and were moral before anyone even thought of the Ten Commandments, see “Religion Functions to Sustain the Moral Order” — Starkly Wrong
The Commandment stuff
- I am your one true God who led you out of Egypt to the promised land. Love your God above all things, and have no other gods before me.
- Do not carve graven images for worship, or practice idolatry.
- Do not take God's name in vain.
- Remember the Sabbath day and keep it holy.
- Honor your father and mother (or mothers, depending on if you're reading this in Exodus or Deuteronomy).
- Do not kill.
- Do not commit adultery (basically like coveting taken to the level of action, which kinda makes this commandment self-defeating in light of the previous one - oh well).
- Do not steal.
- Do not bear false witness.
- Do not covet your neighbor's possessions or wife (especially if you're a woman, because that would open up a whole 'nother can of worms of damnation).
In some versions you can add a commandment that sounds like this:
- Love your neighbor as you would yourself.
That's actually a really good, moral thing to teach to anybody, but unfortunately it only really gets pushed in some Protestant versions of the Bible. Also, some versions split the first commandment above and then delete one of the later ones.  Certain other wikis may have more detailed information, but beware of the extreme atheist bias.
Note that these Commandments are absolutely essential to the U.S. legal system, since exactly two commandments, for a whopping 20%, are adopted into the U.S. legal code, whereas people would never think not to kill or steal without Charlton Heston's divine revelations. (Of course it was OK to smite a whole lot of innocent Iraqis to death when George W. Bush
found weapons of mass destruction in Iraq wanted to please his buddies from the oil industry) Liberals do a better job at following the ones that matter than conservatives, especially when liberals follow the Golden Rule.
The Ten Commandments aren't unique to Christianity or to Judaism
- Congressional quotes on the Ten Commandments
- Ten Commandments & American Law
- Skeptics Annotated Bible on the Ten Commandments