Growing via soil means that the nutrients and water that you will be providing to the plants will be provided to them via the soil, which acts as the medium. Soil retains the water and nutrients which the plants can absorb as and when they need it. In non-soil growth, you can either have rockwool cubes, coco coir, peat moss, etc. as the medium or you can have something like a completely water-based setup where the roots are constantly either submerged in water - or are being provided water with the help of sprinklers. Here, the same water keeps circulating in the system for a while before it is replaced. These systems save water but are expensive and complex to operate.