Atheism and Agnosticism are closely related, but they are not totally the same. Atheism is the belief that no deities exist. Atheism does not believe in the existence of God, and the follower of such belief is always ready to prove the non-existence of God. Agnosticism, on the other hand, is a belief system which doubts the existence of God but cannot prove it. Most times, people tend to criticize Agnosticism for not adequately determine what to believe. This is because Agnosticism will not tell you whether there is God or not.
Atheism has to do with the belief system of people, that is, what they believe and what they don't, while Agnosticism deals with the knowledge about what people know about what they believe. Atheism will give a strong conviction about the non-existence of any god, while you can easily convince those who believe in Agnosticism, provided you can substantiate your claims with facts about the existence of God.
Atheism and Agnosticism are two ways that one can define themselves in regards to their beliefs. Atheism is one who doesn't believe in God or any divine being. While an atheist doesn't believe in it at all, an agonistic doesn't believe or disbelieve in God or any doctrine that is related to religion.
They think that there is no way for all humans to know whether or not there is a diving being or whether or not there is a God. Agnostics also feel humans can't understand how the universe came about and how we humans are here today.