The world is an illusion but it is real enough. The human senses are finite and thus subject to faults, so the world percieved by a human mind is an illusion. However the energy that is the substratum of phenomena is real. The brain identifies may qualities of Brahman and so names them many things. But this is an illusion because there is nothing but that energy, for example a chair isn't a chair, chairs don't exist, what exists is a quality of Brahman that we identify as a chair...
Ive noticed in many posts that people confuse advaita, for some kind of solipsism. The world is an illusion, but its real enough.