Advaita means non-dual. Advaita Vedanta (AV) asserts that Brahman alone is; there is no creation and that the world is a manifestation of Brahman. For a beginner seeker, like me, it is difficult to accept this assertion because the world is perceived and experienced. It constantly stares at me announcing its existence and reality. AV uses a gold-ornament metaphor to make its point. Ornament is a manifestation (name and form) of gold because there is no ornament separate from gold. To this, a counter poser would be that in the gold-ornament example both gold and ornament are material things and are perceived whereas the world is perceived and Brahman is not perceived. Secondly, how can the material world be a manifestation of immaterial Brahman?
It seems to me that the confusion is due to the term ‘manifestation’ as there is a tendency to perceive both ‘manifestation’ and the ‘thing’ that is manifested. It is preferable to explain the matter in terms of order of reality. Brahman is the highest order of reality; creation, though it exists, is a lower order reality borrowing its existence from Brahman. And in this sense only it is said that Brahman alone is; there is no creation, and that it is a manifestation. With this explanation, the metaphor is more illustrative. The existence of the world is not denied, instead, it is mithya. Idealism (i.e., creation is a manufacture of mind) has no place in AV.