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

The writing is one of the most important and most well known lines in American history. What does it mean? Why does Jefferson mean when he says these truths are ‘self-evident’ ?