Oh dear. That's a big question. It would take an essay at least, and different paths will have different perspectives on this that are not identical to my own.
To oversimplify things, consider a vantage point which states there are two basic facets of existence: (1) aspects of reality that can be measured by science and are believed to be objectively real and, (2) aspects of reality that are intangible and often called imaginary, abstract, or ideological. (1) describes "this" world while (2) often (but not always) describes otherworlds.
Again to oversimplify, (1) and (2) routinely exchange things. The idea of a painting is (2) but once painted by the artist becomes (1). The painting witnessed by another could then easily inspire some other intangible abstraction and become (2) again. Ideas can be manifest into the "real" world and the "real" world manifests things into idea-land.
There's more to it than this, but it gets to a level of wonky most folks either can't or don't want to wrap their heads around. >_<; Regardless, it's still a map, not the territory.