Here's my short interpretation/explanation of the physical and astral realms.
We live in the physical realm, where everything strictly follows the laws of physics and where things like flying and shapeshifting are impossible. However through astral projection, we can go to the astral realm/plane, where those things labeled fantasy are possible.
If you'd like a more in depth explanation, just ask.
You ever heard in science fiction movies people talking about dimensions, well this is what a plane essentially is, another dimension. Here we are in the third dimension, the physical plane. It is denser than the other planes and alot more limited. The many many higher dimensions are vastly different from the physical plane. In these planes of existence, matter isn't as set in any given form as it is here, it's more fluid and malleable, and is therefore easier to manipulate with the energy of our thoughts.The astral plane is one you know quite well, since you visit it nightly when you sleep. Does it now make sense why your dreams are so easily governed by your thoughts, and why some seem so real you can feel, smell, and taste everything in it? Beyond that, there are numerous other planes, and each one is lighter and more malleable than the last. Everyone is born with the ability to see into these planes, andare ststartled by this gift with the occasional ghost, shadow person sighting, or imaginary friend relationship as children. This is my understanding. Hope I helped.