John Adams argued for it. Thomas Jefferson wrote it. Ben Franklin got people to like it (or "schmoozed" it). There are 3 parts to it. The first part talks about the rights of man. The second part is complaining about the King. The third part says that the colonies were free.
The Declaration declared the rights to life, liberty, and the pursuit of happiness. This was appropriated from John Locke's 3 natural rights: life, liberty, and property.
It complained about taxes, soldiers living among us, and the King controlling judges.