Whether one believes or not, they can also be comfortable in not claiming to know for sure that it's either true or false.
However, both do not make the claim to have the knowledge to back up this belief.
By now, the difference between being an atheist and an agnostic should be pretty clear and easy to remember.
Atheism is about belief or, specifically, what you don't believe.
Fundamentally, there is still some question and that is why they're agnostic.
This seems contradictory and difficult, but it's actually quite easy and logical.