Atheism settles a single point: whether any god exists. It answers no, or it answers that the case has not been made. Nothing else follows from that answer. What an atheist thinks about the good life, the state, death, art, or what the universe is made of is left entirely open, and two atheists may share nothing at all beyond the one negation. Historically they often have not.
The standard distinction is between the weak or negative form, which is simply the absence of belief in gods, and the strong or positive form, which asserts that no gods exist. The difference matters because the two carry different burdens. Someone who merely lacks belief has made no claim and owes no defence of one. Someone who asserts that no gods exist has made a claim and can be asked to support it. A great deal of argument between atheists and their critics turns on which is meant, and much of it is conducted at cross purposes.
Two things atheism is not. It is not antitheism, the further judgement that religion is harmful and should be opposed; the two travel together often enough to be confused, but they are separable, and plenty of atheists hold the first without the second. And it is not a religion, though the charge is made regularly. There is no atheist scripture, rite, clergy or obligation, and nothing an atheist can be excommunicated from. The stronger version of the charge is narrower and harder to wave away: that particular organised atheist movements have behaved socially like religions, with canonical texts, recognised authorities and internal heresies. That is a claim about movements, and there is evidence for it, but it is not a claim about the position.
Nor does atheism supply a moral code. Atheists have been utilitarians, Kantians, Marxists, libertarians and nihilists. Where morality comes from if not from a god is a real question, and secular philosophy has several competing answers to it; atheism as such offers none of them.