I think that frame can be used to compare our day-to-day experience with experiences that feel like the OTHER side. I tend to think that we can never truly know the OTHER side because we're always in THIS side. In the strongest sense of this frame, the OTHER is well and truly unknowable, and any weird stuff that happens on THIS side may or may not be related to the OTHER, and if it is related, the relationship would be unknowable.
There are a number of useful sources. I like Frank DeMarco's work as a contemporary writer. I also like Stewart Edward White - especially The Unobstructed Universe. Jane Robert's Seth books are also useful. There is a bunch of esoteric and mystical stuff as well.
In fact there is constant traffic between what I call then physical and metaphysical dimensions of our reality - but it is mostly not literal, and tends to be metaphorical according to the content of our psyches. This is why some dreams are absurd metaphors that require interpretation - rarely any good in my experience (unless the interpreter is psychic).
It is actually important to understand that we dwell on both sides routinely, but what comes to our conscious awareness is a small portion of what is actually going on. In fact this is essentially true on this side as well, from a biological and psychological perspective. The sense of I that we have, as the locus of our conscious awareness, is a tiny zone, compared to the physical and metaphysical processes that are fundamental to our physical and metaphysical existence. Our awareness permeates all the processes, but we mostly have no command on locating our point of conscious awareness. We can learn, if we wish, to have greater control over the location of our point of conscious awareness.