The four main pillars of Ayn Rand's philosophical system called Objectivism are reality, reason, self-interest, and capitalism.
The first pillar means that reality is objective. It is not just a social construct. The first premise of everything must be that existence exists.
Reason is humanity's asset in the all too real world. We have to consciously choose to employ it.
Self-interest is Rand's protest against the conventional, hypocritical morality. In her view, we must give up on living for others, or for causes. Our self-interest is our ultimate goal and motivator.
Capitalism as an economic and social system is for Rand the perfect embodiment of liberty. Of course, governments mustn't interfere; it has to be a laissez-faire capitalism.