While written many years ago this remains the best description of what libertarians believe that I know of

…all human relationships are voluntary. Men are free to cooperate or not, to deal with one another or not, as their own individual judgments, convictions, and interests dictate. They can deal with one another only in terms of and by means of reason, i.e., by means of discussion, persuasion, and contractual agreement, by voluntary choice to mutual benefit. The right to agree with others is not a problem in any society; it is the right to disagree that is crucial. It is the institution of private property that protects and implements the right to disagree”

Ayn Rand, “What is Capitalism?” from Capitalism the Unknown Ideal