What a fantastic question!
I won’t (and can’t) get into as much detail as I’d like, but I will tell the basics. Everything in the universe is a form of energy. Energy of some kind, and vibrates at various frequencies. Lower frequencies are solid matter, for example, and the higher frequencies are what we call spirit. God, of course, it the highest of all, the purest and highest form of energy, the Source of all.
Spirit is basically a particular form of energy within a certain range of frequencies. No one can really tell you the EXACT frequencies, but they are far above human experience without being open to that level. Spiritual energy is known by many names all over the world, and people have been perceiving, and trying to describe and use, this energy for thousands of years. For example in martial arts there is ki (in Japanese) or chi (in Chinese) and prana (in Hindi) and many other names over the years.
Spiritual beings, however, are not just energy, but like human beings a collection of things, organs, substances, and levels of energy. Our bones, for example, the densest matter, is at the lowest frequency of energy, the liquids higher, our emotions higher than that, our thoughts above those. Our human spirit is a “body” of a collection of different energy forms, organs, if you want to call them that, things that make up our spiritual body or form. Other spiritual beings don’t have bodies, but the spiritual bodies, which are energy forms of various kinds that make them up.
We humans don’t fully understand these things, and sometimes people like me take an interest in this phenomena and can only try to understand and piece things together from experience and the writings of ancient people who tried to understand them in the only ways they could. For example, God. We can only think of a being like this as the Highest form of spiritual energy of all. Below him are “angels”, beings on somewhat lesser frequencies or levels of vibration. And they go farther down the levels of vibration or frequency, down to what ancient people called “demons”, the lowest of spiritual entities. Then we have humans, who are not only spiritual beings but inside a physical body, and develop a “soul” through life. Below us are animals, then all the other critters in creation, then non-living things.
There are so many books on this and so many opinions, pro and con, that one has to study and consider what makes sense to them, and not be dogmatic about it. After all, we can’t really know until we are no longer in physical bodies and enter the spiritual realm personally. We have to take the word of others who studied this before us and test it. For example, there was a recent question about chakras. These are places that interface with the physical body made of energy, and a concentration of this energy at a particular range of frequencies. A chakra is a wheel, a vortex. But it seems imaginary because it consists of this spiritual energy people have always been perceiving, but just can’t fully understand or prove to everyone’s satisfaction.
