To know the difference between atheism and religion, you must look at the meanings first. Atheism means the belief that there is no God or supreme being. Religion means beliefs on how the universe was made, usually by God or some supreme being. The main difference would be to say that atheism believes there is no God/supreme being, and Religion refers to the belief that there is a God/supreme being.
The word Theism means a belief in one God that creates the universe. Now its hard to believe that if you just add an A to theism then you get lack of belief in God. The word atheos also means a lack of belief in God, atheism originates from the Greek word atheism. The word religion is a English word coming from that Latin word religio. Some people think that Atheism was developed because of Christianity. The word religion has been used as early as the 13th century. The word atheism has been used as early as the 15th century that we know of.
Many atheists today and in earlier times have argued that religion is nothing more then emotional and psychological wants and needs. But at the time of atheism emerging, it was considered bad to be an atheist. While that happened, Christianity and other religions started to spread through out various places. Religion consists of many different sorts of groups that form a religion like Christianity, Buddhism, Judaism, Hinduism, Islam, and more. While Atheism is not classified as a religion, but is just a certain kind of group or way all by itself.
Atheism has said to be related to evolution, but that would mean that only atheists could believe in evolution. So that means someone who believes in God or a supreme being could not possibly believe in evolution. Which then comes back to having belief for something that created the universe. In order to have belief, you must have faith. And again atheists argued religion is nothing more then emotional and psychological wants and needs, which can be connected to have belief or faith. This all states a major difference that Religion can be referred to as belief and faith, as where atheism or atheist philosophers are against beliefs and faith. Karl Marx argued that belief in god is social functions.
In our time atheism is more widely accepted, but not as big as religions such as Christianity. Either way it seems that atheism and religions will have problems for the rest of their existence.