The astral plane is a spiritual reflection of the material world. Technically, every time you physically perform a spell, you are also working on the astral level. A physical action in a spell is performed specifically for the equivalent and associated energy where it means on the astral plane. Once you have become adept at handling energies gathered in the physical world, then you might find yourself using fewer and fewer props and components. The web of energy, which connects everything, also extends to the astral level. It’s perfectly possible to do an entire spell on the astral plane, which is where most change occurs anyway, initiated by your symbolic actions on the physical plane. It take a lot of focus, and the establishing of a personal place of power on the astral plane.
You’re most likely familiar with the astral plane due to the concept of astral projection. The art of astral projection involve sending your consciousness elsewhere. It takes a lot of energy and concentration to do it, and it usually prefaced by meditation. Basically spellcasting on the astral plane is rather like doing the spell in your head, but with all the awareness and intention of performing the spell in the physical world.