It holds that people should be free to live their lives any way they choose, so along as their conduct doesn't involve the initiation of force or fraud against others. In other words, no murder, rape, stealing, burglary, trespass, fraud, robbery, or other action that infringes on the rights of others to live their lives the way they choose.
Thus, libertarians advocate the dismantling, repeal, or abolition of every program, law, department, or agency that is based on the initiation of force.
Example: the war on drugs and the DEA. Since people have the right to live their lives the way they choose, they have the right to ingest whatever they want, no matter how harmful, damaging, unhealthy, or irresponsible it might be. Therefore, drug prohibition is illegitimate under the libertarian philosophy. Drug laws should be abolished, along with the DEA, the agency charged with enforcing the drug war.
Unfortunately, for the past 30 years there has been a segment within the libertarian movement that advocates reforms of America's welfare-warfare state way of life. What's wrong with that? Nothing per se. People have the right to advocate whatever they want.
The problem, however, is that reform-oriented libertarians have couched their reform proposals as "libertarian" when advocating them to the general public. In the process, they have diluted or corrupted the libertarian brand of principled libertarianism. That's why today many people have no idea what libertarians stand for or, even worse, are convinced that libertarianism is nothing more than a rightwing philosophy.