Declaration of Independence: What does the pursuit of happiness intend and mean? Who decides how and what we pursue for happiness?

That's in the U.S. Declaration of Independence, dated July 4, 1776. People have written quite a lot about this, but the salient point, I think, is that it doesn't imply that it's the government's "job" is to provide any sort of happiness to the people so governed. That's up to you, however you define it. It simply recognizes the natural state of human liberty and the right to define and pursue it for yourself. We abuse and confuse the idea quite a bit, in my view, but the concept remains important. The government's job is to defend your liberty, that is all. Note the automated form of internal revolution built in to the text as well. Rather than eternal government devolved from a supposed divine right (i.e, monarchy), the framers wanted the new American government to be on constant notice from its own people. Happiness is that important. The full version reads thus: "We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness.--That to secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed, --That whenever any Form of Government becomes destructive of these ends, it is the Right of the People to alter or to abolish it, and to institute new Government, laying its foundation on such principles and organizing its powers in such form, as to them shall seem most likely to effect their Safety and Happiness." Beautiful words, eh? Also worth noting, the original Thomas Jefferson draft read "We hold these truths to be sacred and undeniable." As the story goes, Ben Franklin was asked by Jefferson to review the text. He made only a few changes, but this one was important. Ever the scientist, Franklin scratched out "sacred and undeniable" and substituted "self-evident." (Source: Walter Isaacson's Benjamin Franklin: A Life)

From what I've always understood the phrase "the pursuit of happiness" is a euphemism for the right to acquire and own property. Jefferson cribbed the moral foundation of the Declaration from the work of John Locke who wrote specifically that the governments role is to protect people's "life, liberty, and estate". For whatever reason Jefferson replaced estate with "pursuit of happiness".

The whole point is that the individual retains the right to define happiness for himself, and the right to pursue it in his own way.