“There is only one fundamental alternative in the universe: existence or nonexistence—and it pertains to a single class of entities: to living organisms. The existence of inanimate matter is unconditional, the existence of life is not: it depends on a specific course of action. Matter is indestructible, it changes its forms, but it cannot cease to exist. It is only a living organism that faces a constant alternative: the issue of life or death. Life is a process of self-sustaining and self-generated action. If an organism fails in that action, it dies; its chemical elements remain, but its life goes out of existence. It is only the concept of ‘Life’ that makes the concept of ‘Value’ possible. It is only to a living entity that things can be good or evil.” -Ayn Rand
A living thing is the only thing to which values are possible. The alternative it faces is remaining alive or death. This alternative is fundamental. It underlies all others. To pursue any other goal one must first obtain what it must to remain living.
For a human being, acting be reason and not instinct, actions and goals must be chosen. Man does not pursue his values like animals, automatically. He can choose to pursue things which are disadvantages to his fundamental goal. He can actively work to do things which inhibit his ability to live. Or he can outright kill himself purposefully. Because he acts by reason he needs principles to guide his actions. He needs an explicit understanding of what improves his ability to live and what hinders it. He needs an understanding of the abstract kinds of things which are good and bad for him. If a person wishes to live and live well he needs a rational ethics.
If someone is to remain alive he ought to pursue certain goals.
Life is the standard of value for anything living. What keeps a thing alive is the good, for it. Plants must pursue sunlight, water, nutrients etc. These are it’s means of survival. Animals need food, water, shelter from the elements. They survive by means of percepts, instincts, memorized behaviors, etc to gain what they need to live. If a person wishes to live they must act also in accordance with their means of survival. And for a human being this means in accordance with reason. Rationality is man’s basic means of survival.
Man must think, and think clearly, to obtain the things he needs to remain alive. The rational then is the good. Rationality requires a refusal to fake reality, this means it requires honesty. His life requires material means, he must think and then act on his thoughts to produce them. He must be productive. Etc. Abstract values, moral principles, implied by man’s basic means of survival to guide his actions. The standard again is that which aids life which means that which is rational.
Lying is bad under normal circumstances; for various reasons it is against your interests. But in a circumstance where you must lie to protect a value, to keep what is yours by right, from someone who is, in the act of wronging you, himself faking reality: In such a case it become in your interest, for your life instead of against it, to lie. Like the example of a man that is wielding a weapon, is trying to kill your wife and asking where she is. Clearly a lie is what is moral.
It is bad to kill people, normally. When they become a threat to your life or someone else’s this changes. In the above example this could be a better choice than the lie if your wife is a value.
This is just a quick overview. It is Ayn Rand’s revolutionary arguments as I understand them. For a fuller understanding see: Viable Values, Ayn Rand’s Normative Ethics; The Virtuous Egoist (both by Tara Smith), The Virtue of Selfishness by Ayn Rand, Loving Life by Craig Biddle, Objectivism In One Lesson by Bernstein and/or Objectivism The Philosophy of Ayn Rand. Probably forgetting something but any of those should work.