As an atheist, you believe/accept that a mindless natural process that has no goal, purpose or direction produced all life on earth.
Atheism is just a response to a claim: is there a god?
Theists/Deists say "Yes".
Atheists say "No".
That is the limit of the discussion. There is no aspect to that reply that makes any statements in regards to purpose or a goal. It is no different than asking someone if they think bigfoot exists. It is a straightforward answer to a straightforward question.
Regarding anything beyond the original ask: that now delves into the realms of religion and philosophy. But note that there are religions out there that have specific beliefs and "meaning", but they don't have gods associated with them. Many eastern religions for example focus more on life energies (Chi) or reincarnation without any notion of a god or an afterlife associated with them. So these are "atheistic" religions yet they have the concept of purpose.
That is why ascribing added arguments to what an atheist "believes" makes no sense any more than me making arguments about what your particular religious faith believes. Because theists may all agree that there is a god, but they
disagree on the meaning, wants and tenets of that god. Even among Christians, there is no consensus. And when you spread that out to alternate religions like Islam and Judaism, the meanings differ even more.
And we haven't even gotten into the discussion about polytheistic religions like Hinduism, Pagan Greek or Pagan Norse. You believe in Yahweh and they might believe in Odin, Thor, Zeus and Hera.