The Second Amendment is as follows:
"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."
This means that people have the right to ownership of weapons (such as guns) in order to protect themselves, as well as the state having an armed and regulated Militia (old term for an army, basically) to protect the citizens and the state.
The final line "shall not be infringed" means that this right may never be removed, changed, etc. as this amendment's main purpose is to protect citizens and the state through means of being armed.