No matter where you go, somebody is going to have some rules for you to follow.  No exception here.  The United States Federal Communications Commission (FCC) is the authority on not only ham radio regs, but also those involving television and radio transmission, telephone company operation, cellular phone transmissions, and a wide range of other communication venues, as their title implies.  Although I believe that government involvement in ANYTHING should be kept to a bare minimum, it's good to have some regulatory body in this case, because somebody has to ensure that radio frequencies are specifically allotted to different types and groups of communication devices. Otherwise, you could hear me transmitting on my two-meter mobile while you're listening to the Bee Gees on your favorite '70's station, and I might end up hearing you and your buddy ragchew right in the middle of the X-Files! 

All ham radio regulations are listed in the Code of Federal Regulations (CFR), specifically Part 97 of Title 47.   Below are some of the important points that are spelled out in reference to general rules that ham radio operators must follow.

Who can become an amateur radio operator in the United States?  Anybody - with very limited restrictions.  Only representatives from foreign countries are prohibited.  There are no age restrictions for operators, so even the very young qualify.  I have heard that children as young as seven have obtained a license.  That should be a motivator for anybody trying to get a license - if a child can do it, then so can you!

Hams can only use the amateur radio bands for the purpose of emergency communications, training in amateur radio science, communicating with other hams, technical studies and testing equipment.  Which leaves the service wide open for many an opportunity.  However, these bands are specifically off limits to business communications.  This includes calling your boss or subordinates about job-related information, ordering take-out, you know - things of that nature.  Hey, if you gotta do that - use a phone, you'll have better results anyway, and you might even avoid the transmission of sensitive information.  The only exception for the average ham user is if you are a non-dealer and you want try to sell or buy radio equipment occasionally.

Your license entitles you to operate your radio equipment; according to the FCC regulations and technically speaking: you, the control operator, will be transmitting from the control point of an amateur station with an amateur operator / primary station license that has been kindly granted to you by the FCC.  Nifty terminology, isn't it?  This also implies specific responsibilities for the operator - you have to ensure that your equipment is safeguarded to ensure that not just anyone can walk up and start transmitting.  You can and will be held responsible if it is proven that you were the disruptive source.  You also have to learn to use your equipment properly, to ensure that you are causing spurious emissions (different types of interference).  And something else: intentionally causing interference with another ham's transmissions or reception is a huge no-no.

When transmitting on a station, you actually have to be communicating with another ham - no broadcasting to a general audience.  Which also means that you can not pick up your harmonica and belt out the blues - no "musical" transmissions.  Another bad idea is to use foul language, so please watch what you say.   Anybody and everybody can hear you when transmitting on amateur frequencies, including children.  Also, impersonating another amateur for malicious intent is prohibited, as well as sending coded messages (that's very ambiguous to me since this hobby grew out of the art of Morse code).

Why must you pay close attention to all of this?   Reason numero uno: COURTESY - to all other fellow hams.  And secondly, it would be pathetic to go through all of the trouble of obtaining your ham ticket, buying the equipment, falling in love with a great hobby, and then having your ticket yanked because of the AIS phenomenon (adolescent irresponsibility syndrome).

For the newcomers, you may begin transmitting after you have been granted your callsign, similar to the four-letter phrases that your local TV and radio stations use to identify themselves with.  Receiving your own callsign indicates that your license has been officially processed and that you are now recognized by the FCC as an amateur operator.   Basically, your callsign will become your name, for all practical purposes.  So now you can transmit, but only for the privileges that your license class allows.  However, you are not tied down to operating just one piece of radio equipment, as the term "station" implies.  You can operate any equipment that operates on the frequencies within your license privileges.  You can operate on more than one station, even somebody else's (although they are required to be there to ensure that you are following the rules).  You can communicate with other operators outside of the US.  The key point - operate only within your privileges.