Gardening without using soil is called hydroponic gardening. Most often water is utilized in hydroponics, consequently the name. No doubt you could find a more technical explanation of the process. But the ordinary gardener doesn’t really need more knowledge than that.
Maybe you’ve questioned how you can raise plants hydroponically with no soil. It is generally supposed that plants must have soil. It provides nutrition, physical support, energy and water. These are all necessary if you want the plant to thrive. However these elements are also available from other sources.