It guarantees, "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." The need for a State militia was the predicate of the "right" guarantee, so as to protect the security of the State.

Which amendment is the most misunderstood?

The Eleventh Amendment might be the most misunderstood amendment to the Constitution.

What is the biggest controversy surrounding the Second Amendment?

Perhaps the biggest open question after Heller is whether the Second Amendment protects a right to carry guns in public. While every state allows public carry, some states restrict that right to people who can show a special reason to have a gun on the street.