This page is under development, but at the outset, in my opinion, the essence of atheism is a belief that the supernatural either does not exist or is of no importance to the natural world, including humans.
Behind all religious beliefs lies the assumption that there are forces outside of nature that control, guide and/or explain the natural world. But, is there or can there be anything outside of nature - does anything supernatural exist or can anything supernatural exist? Atheists are generally unanimous in believing that the natural world is effected only by natural forces, whereas religionists generally will appeal to supernatural forces to explain the mysteries they see in the universe. The "transcendental temptation" is great when people do not know why or how certain things happen in nature (more on that concept later)!
It seems that the issue can be solved philosophically and scientifically based on the fact that no supernatural force has ever ever been observed in the natural world. Many have claimed that they have seen the effects of the supernatural, but when the causation of any of these effects or mysteries has been found, it has always been found to be entirely explained as natural phenomena. So, if the the supernatural exists, but never comes into the natural world, then it is not of any importance because it does not affect us. The only other explanation for the lack of apparent supernatural intervention in the natural world is that the supernatural simply does not exist.
Religionists like to rely on faith as the foundation of their beliefs, but I must point out that faith is a meaningless reason by which any belief should sustained. Faith is just hopes and dreams without any method of proof.
Eventually, I intend to present detailed explanations in response to arguments that theists make in support of their contentions that the supernatural and their god or gods exist. In the meantime I refer you to three organizations devoted to the advancement of atheism: