Some use them for hunting, self defense, crime or a symbol of freedom in america.
No country can be free without the civilians having the right to bare arms against it's own government when the need arises.
There are two types of guns used by most.
Rifle: a gun used for long range and accurate shooting.
Handgun: Used for close quarters, and so you can carry it so you don't advertise to the world you have one. To conceal it you must take tests, written and field to get a permit.
There are other variations but the ideas for them are derived from those two.
Assault rifle: Usually has multiple settings for firing. Single shot for accuracy, triple for chest to head shots to be sure they are going down, and fully automatic, which is typically used for creating cover fire or close quarters.
Sub machine gun: compact easy to move around corners, favorites of swat.
Shotgun: Uses shells filled with buckshot or slugs. Typically buckshot to have a spread. Open choke is used for very close range with the highest spread. Closed for longer shots such as bird hunting, and one for in between to have the best and worst of borth options.
Machine gun: Made to fire many rounds, and not much else.
Stupid people shouldn't own guns, because they will blow your face off.
When a police officer readies his gun for a killing shot, he may experience tunnel vision and lose awareness of everything around him. That is if it bothers him psychologically.
They come in small, handheld forms known as pistols or handguns; or automatic, repeating-fire, styles known as machine guns; and longer types with stocks and that are designed to be fired from the shoulder: these are known as rifles. The many kinds of guns, the mechanical/technical information of a gun, and so on are WAY too long to list here. For additional information I recommend looking at the other examples below.