Atheists are individuals, as are theists. The ONLY thing we all have in common is not having a belief in any deities.
I don't believe because there is no evidence of a deity. Same reason I don't believe in fairies, elves, leprechauns, werewolves...
Some of us do gather together. There are atheist organizations, atheist conventions, etc. We also gather with our fellow humans outside of this one belief, just as most theists do.
Without a belief in a deity and an afterlife, life itself becomes much more important, much more precious. Without a god to forgive me or a devil to blame, I alone am responsible for my behavior, thus, I aim for high ethics. I believe in compassion, altruism, love, joy, civility, education, critical thinking, friendship and more.
Atheists have the full range of human emotion, human need, and human experience. The only difference between us and theists is that belief in a deity.
~Atheist, ex-Christian, former new ager