The nutrient film technique or 'NFT' hydroponic system can appear complex at first glance but is actual fairly simple to understand in concept.
It consists of angled channels on which plants sit with their exposed roots freely hanging in the channel cavity below
Water is then pumped down the channels and it flows over the plants' roots providing them with the nutrition they need to grow.
The key feature of a nutrient film technique system is the constantly flowing supply of nutrient-rich water. The channels that supply the roots with water are slightly angled, so the water itself is always flowing and moving, creating a thin nutrient "film". This means that the water can provide a constant supply of fresh nutrients as well as remain oxygenated. Just like people, plants also need oxygen to perform respiration and provide themselves with the energy they need to grow.
As far as the mechanics of the nutrient film technique system go...