Carefully consider your available space, lighting, budget, and time constraints before purchasing any equipment or settling on a unit to build yourself. Also think about what you want to grow, whether you may want to expand, and recurring costs.
Active systems rely on a pump to flow nutrient around the plant's roots and to provide aeration.
Passive systems work without a pump. A wicking material draws nutrients up to the roots or the root tips are suspended in a stationary solution with the main portion of the rootball hanging in the air. Most operate on timers, alternately wetting the medium to wash out salts and replenish nutrients and then draining so the plants can draw in atmospheric oxygen. Water culture systems usually operate without media. Sometimes rockwool cubes or small amounts of gravel are used because plants like tomatoes and cucumbers get top heavy when they start to bear fruit and may need help to stand upright.