Theism is a worldview which states that there is a God who created the world, and he is present and helps us in the world. The worldview Theism includes the religions Christianity, Jewish, and Islamic.
Atheism is the complete opposite of Theism, for Atheists believe that there is NO God at all and that there is no hope for us; while Theists think that there is a lot of hope.
Two other worldviews are Deism and Materialism. Deism is a worldview of which people believe that there is a God, but he does not interfere with the world. Deism was started in an intellectual movement around 17-18th centuries. Materialism was a worldview of which that all things are made of material, and is all about how much you own, and says that material is the only substance, but not too far as to say that there is absolutely not anything spiritual, its just that they believe that Materials are the most important thing of all. The differences in these worldviews are quite large, but not as much as Theism and Atheism.
Worldviews are a very important part in our lives, and I now always find the worldviews in the books I read.