Question

what does it mean in the Declaration of independence when it says "governments are instituted among men to secure these rights?"

Answer 1

This refers to the rebounding aspect of social contract -- on the government's behalf of course -- in which the citizens have the power to overthrow or replace a government if it misuses its powers, breaking the social contract.

This quote in particular states that it is the government's duty to protect the rights of the people -- rather than taking advantage of the people.