The 2nd amendment is in the bill of rights (NO SHYT). It states: 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.

It consists of three parts, and one reason:
A well regulated militia,
The right of the people to keep and bear arms,
Shall not be infringed,
- Being necessary to the security of a free state.

A well regulated militia -
It's important to understand the complete difference between a militia, and a military. In term a militia is an army, but composed of ordinary citizens rather than professional soldiers. It must be further understood that it was angered, and oppressed ordinary people who’s ages ranged from 16 up until old as hell whom took possibly the greatest toll against the government at the time of the revolutionary war.

The right of the people to keep and bear arms -
In accordance with fact, reason, or truth; correct, derived or coming from; originating at or from, humans considered as a group or in indefinite numbers, in a direction toward so as to reach: to retain possession of, together with or along with, any of various usually omnivorous mammals of the family Ursidae that have a shaggy coat and a short tail and walk with the entire lower surface of the foot touching the ground (joke, replace this part with the word hold (the bear joke)) a weapon.

Shall not be infringed -
May not be changed.

Being necessary to the security ...

In casual usage, normally refers to the right to gun ownership in the United States. The Second Amendment is often invoked when discussion is about a gun being used in commission of a crime, or in self-defense. Over time, it has been perceived as a "gun owners" specific amendment. It is one of a list of rights that The People do not cede to the Government, such as free speech, freedom of the press, freedom of religion, no self-incrimination, no forced quartering of troops, and so on.