Of course there are way more than three planes in reality and each plane isn't really "above" or "below" one another like many would have to believe, but for now we'll focus on keeping it relatively simple, so we'll only go over the three commonly known planes for now... Of course there are others, such as the void, the pantheon realms, etc.

The physical plain that we all know and love considering that we are currently living on it... So there isn't really a way that you don't know exactly what this plane is.... This plane is a "solid" plane but is different than say the Etheric due to a lack of energy being able to manifest on it due to how this specific plane functions... So we instead normally rely on different methods here to design and create technology/understand the universe due to it being fairly different from a lack of energy manifesting here...

The Etheric plane is another "physical" plane but has some key differences... First off energy can manifest on it as if it was a solid itself, while of course it is just a different form of matter. (On the physical plane it it IS here, just not manifesting in a tangible fashion nearly as much)... But anyways there are many other differences, but keep in mind the Etheric is closely connected to the physical... So there is a etheric side Earth, and most other planets are on each side... As above, so below you could say....

The Astral is the third plane we will be quickly discussing... The Astral is a plane that is purely made out of "thoughts" and is mostly what could be called an Imagination plane... Thoughts can manifest instantly and change the whole landscape of it in a second... People will often see different things for the same area, etc. And it is rather imprisoning meaning the longer you stay there, the harder it is to get your projection sight out of that region... So personally I would suggest staying out of it, as it is mostly just a way to lead yourself into delusion.