The Second Amendment guarantees the right of the citizenry to keep itself armed and thereby capable of overthrowing a federal government turned tyrannical.
These days, the right to bear arms is caught up in issues of personal firearms. The 2nd Amendment might or might not protect a citizen's right to own a handgun or an assault rifle. If it does, it also protects the citizen's right to own a howitzer.
Defenders of gun rights cite the utility of handguns in protecting the private citizen from crime. This argument is utilitarian. If the argument is valid, it means that we should be allowed to have handguns regardless of whether our right to own them is guaranteed by the Constitution. That argument has nothing to do with the 2nd amendment.
The authors of the US Constitution were not thinking about crime when they wrote the 2nd amendment. They were thinking about armed revolution. They had just won their own revolution, and they did not begrudge future citizens the right to overthrow their own government.
Handguns and other personal firearms are handy for acts of terror by small groups or even individuals, but they would not be sufficient for overthrowing the federal government. That's why each state has its own militia with real military hardware. Militias are for defense of the state, whether against a foreign invader or against a "domestic" enemy. As the federal government has increased in political power and moral stature, however, the role of the militia as a way for citizens to protect themselves from Washington, DC, has been downplayed.
The 2nd Amendment is why the southern states were able to secede from the Union and make it count. I don't mean by this statement to say that the 2nd Amendment is bad. I merely intend to demonstrate the historic significance of the amendment. The 2nd amendment isn't some abstract legal principle. It made the US Civil War possible. Personally, I wish that the southern states hadn't seceded, but that's another rant.
Does the 2nd Amendment protect one's right to own a firearm personally? It does, but only insofar as it also protects the citizen's right to own brew and store ricin (a biological poison). Which is to say, "Not unconditionally."
This rant has described the 2nd amendment but I've avoided the straightforward issue of whether citizens should be able to own handguns. In the interest of completeness, I should state my position. When I look at the US as part of the first world, I see that we stand out in two ways: lax gun control and sky-high gun deaths. I'm sorely tempted to add 2+2. Still, I haven't ruled out the possibility that 2+2 = 5. It's possible that gun deaths are high in the States for cultural reasons, and that gun prohibition would be ineffective.