You see the news and watch TV shows like Cops and you start to think that every American is packing a weapon. If you do not live in the US, you probably have not heard of or seen Cops because it does not give an accurate impression about the US. The media shows the most dramatic, TV worthy images for the viewers pleasure.
The basis for public firearms ownership is founded in the US Constitution, namely the Second Amendment. The wording is as follows. "A well regulated Militia being necessary to the security of a free State, the right of the people to keep and bear Arms shall not be infringed." Some feel this is an individual right, giving the 'people the right to keep and bear Arms' whereas others feel the right is more collective, giving the state the right to 'regulate a militia'. In 2008, the Heller decision by the Supreme Court ruled 5-4 that the 2nd Amendment was an 'individual right' and thus, could only be restricted in very limited circumstances (as compared to a collective right of a government to maintain a militia, as the opponents had argued). The Heller decision struck down a total handgun ban that was in place in the nation's capitol of Washington, DC.
At a national level, about 45-50% of households have guns (exact numbers are difficult to obtain) and there are more guns in American than there are people. As you might expect, ownership numbers really depend on where you are living. In many rural areas, people WITHOUT guns are the exception. Gun ownership in some rural counties is nearly 80%. One possible reason for higher ownership is that the firearms are used in the hunting of deer, wild turkey, bears and other creatures. To some farmers, a gun is simply a tool, used to control wild animals that sometimes threaten their herds. In some major cities, there are legal bans on owning firearms such that a very small minority actually have weapons.
You will probably never see a gun in public in the US, unless you live in a hunting area (like rural Pennsylvania), go to a gun show, a firing range (some which requires membership) or a store such as Walmart, Dick's Sporting Goods or a gun shop.
It is probably worth noting that the use of a firearm to defend oneself is legal in many parts of the US, so long as the person has a 'justifiable fear for his life or the life of others.' In many states, a person has the obligation of retreat first (unless in their home) before they can defend themselves, but 'justifiable homicide' does occur when a person kills another to prevent their own death. It is often remarked anecdotally that many a pub flght in the UK would end as a gun fight in the US (which may be why some people see fewer incidents of public fighting in the US, though it does occur).
The purchase of a legal firearm varies from state to state. (see http://www.statemaster.com/graph/gov_gun_law_per-government-gun-laws-permits). Some require permits to purchase. There are eligibility requirements to purchase and consequently own a firearm legally. Generally, those over the age of 21 may purchase a a firearm from a federally licensed dealer in the state where he/she resides.
If you are on non-immigrant status there are special federal firearms rules and you are usually required to have a valid hunting license from U.S. state as well as comply with any additional state/local laws.
Green card holders are not subject to federal restrictions on firearms. Most states and localities do not place special restrictions on GC holders (over and above those applying to U.S. citizens) but there are exceptions.
Each state determines its own concealed carry laws. The majority of US states permit concealed carry (in most cases with a permit) but some restrict concealed carry, notably California and a number of states in the North East. A minority of states make having U.S. citizenship a condition for eligibility for a permit, but several such laws have been changed as a result of successful challenges in Federal court, under equal protection doctrine. Alaska, Arizona and Vermont do not require any permit to carry concealed.
Personal experience of BE Member obtaining Guns in Colorado as a LPR. Select your weapon, complete Background Check form, you will need DL and GC, sometimes it is a paper form, sometimes a computer terminal. Wait for approval, seems it takes longer for LPR but usually within the hour, pay, exit with your gun. Ammo does not require anything special, they may ask for your DL to check you age, If buying in somewhere like WalMart you pay at the Sporting Goods counter.
Concealed Carry Permit requires a course which can be quick at a gun show or hosted by a gun store or day long which is recommended for those new to guns. You then take your approval to the local Sheriff Dept, FBI check requiring finger prints and within a few weeks are sent your Permit.
Hunting usually required a Hunters Ed class which is usually a day and includes a practical section.
You can buy online and have a gun sent to a local dealer, also a usefull shopping tool, see http://galleryofguns.com/ as an example.
Brady Campaign Website
National Rifle Association Website
U.S. Treasury Bureau of Alcohol, Tobacco & Firearms