Ok since we've covered nearly every word of that sentence, lets review it as a whole.
A well regulated militia being necessary to the security of a free State
So, ther militia is necessary to the security of a free state. Then, where's the militia ? Some of you might say that the militia is the people. Then who or what make sur that the militia is self regulated. When people with diagnosed mental issues can buy any kind of guns, the militia is not well regulated.
The Founding Fathers wanted US citizens to have the right to own guns so they would be able to defend the nation against dictators and other authoritarian regimes. They wanted the people to form a militia and the militia to be welle regulated. They wanted guns owners to be trained is the use of guns, they wanted the community to make sure that people who coudl represent a threat to the community and it's members wouldn't not to be able to buy guns.
But when there's no well regulated militia, then the sole purpose of the right to bear arms fades away.
2) The Right of the People to bear arms shall not be infringed.
It says "the right to bear arms". It doesn't say "the right to bear any kind of arms" So, basically you coud argue that the people have the right to bear RPG, tanks, cluster mines, etc... But you could also argue that people have the righyt to a reasonable fire power : pistols, rifles, shotguns, etc. but no assault-rifles, not sniper rifles, no body-armor piercing ammos, etc.