A well regulated militia
- armed and drilled common folks. This is not a standing army (which is constitutionally prohibited) or a national guard/reserve that is armed by the government. If the founders had meant this, they would have not needed the 2A as the arms would be provided by the government to the forces.
being necessary to the security of a free state
- attacks on the free state can come from a variety of fronts. They can be external or internal. The founders had the foresight to allow the citizens to arm themselves to ward off these attacks. Many foreign foes have eschewed attacking the US on its own soil because they, rightly, assumed that there would be a citizen with a gun behind every tree. We have not had many attacks on our soil as a result of this, and other, strategies. If the attacks to the government come from internal sources, an armed citizenry has the ability to hold the government in check - it would be bloody, but it still could be done.
the right of the people
- The people, we the people, includes citizens and can arguably be inferred to include legal aliens in our midst. This is elsewhere acknowledged as a fundamental right that comes from our Creator, not the government. The 2A is in the Constitution to make it clear that the founders knew that neither they or the government were creating a right, but simply making sure that future generations understood the right and that to change it, would have to go through the amendment process which requires significant efforts.
to keep and bear arms
- Keeping arms is the process of procuring, maintaining and storing them. Bearing arms includes transporting, wearing and using arms to protect oneself (self defense) or the country (war or insurrection). Arms include weapons and the ammunition to operate them. While the common perception of arms is that they are small arms, some would say they have to have a sporting or SD purpose, the Constitution does not limit the arms the populace has the right to keep and bear. If the founders had meant to define arms to be small arms, they would have ruled out cannon, ships and other artilery types of weapons that were available at the time. That they did not limit the categories of arms that the populace can keep and bear means that, if you could afford one, owing a fully armed F-15 would be constitutional.
shall not be infringed
- The 2A is a limitation on government, not the people. Shall not be infringed means that the government cannot put any infringements on the rights enumerated in the 2A. This is the part that the Feds violate more than the rest. Your right to bear arms on almost any federal property (except parks) has been eliminated, removed - infringed. Prohibitions for carry at federal courts, office buildings, schools, etc. - all are infringements on the 2A.
So, in a nutshell, the 2A acknowledges the natural right of citizens and legal aliens to buy, store, maintain, transport, wear and deploy arms in defense of self and/or country. This right comes from our Creator and is simply affirmed, not created by the Constitution. The government, federal, state or local, cannot make laws that keep citizens or legal aliens from exercising these rights.