Terahertz range lies in between the microwave and the infrared one. It is one of the last frontier of the photonics world where sources and detectors are less efficient more bulky and expensive. Still advances of the last decades enabled to use terahertz system for real life applications with the notable example of several providers in EU proposing tools to measure the thickness of the paint during the painting process in the automotive industry. Terahertz spectroscopy has much more to offer for example for quality control in drug or food industry where molecular crystal give very specific signatures, or in aerospace to measure the water quantity in the oil used in the hydraulic circuits and avoid costly and useless systematic change of the oil. Finally, THz spectral range is the fingerprint rovibrational range of light molecules. In this range, most of volatile organic compounds have a precise strong and define fingerprint. Those compounds are involved in many industrial and environmental processes and THz technology could be a key for the air quality control or for health application in so-called breathalyze. In this training, we proposed to give a practical overview of what can be done in Terahertz spectroscopy on the three different phases, solid liquid and gas phase.