Materialists believe everything reduces to material stuff - atoms and the particles of which they are made. On this view, even phenomena like ideas and sensations are merely epiphenomena of the material brain. The brain, in other words, is all that's necessary to explain mental events. There is no mind.
This view is becoming increasingly untenable, however, as we learn more about the deep structure of living things. It certainly is beginning to look like matter is itself reducible to information and, since information lies downstream from mind, it would follow that immaterial mind is even more basic than matter.
The following video is a bit long, but it illustrates how the theory that matter is reducible to information plays out in biology. It's pretty good.
Perhaps the 20th century physicist Sir James Jeans was correct when he said that the universe is beginning to look more like a great thought than like a great machine.