Bhandas are energy locks. It is done through tensing certain muscles group, to increase the flow of prana (energy) within our body.
There are 3 main energy locks, root lock (mula bhanda), diaphragm lock (uddiyana bhanda) and neck lock (Jalandhana bhanda), applying the 3 locks together will form the great lock (mahabhanda).
Some of the functions for the 3 bhandas are as follows :
Root lock (mula bhanda) simulates energy of the lower chakra and transforms it to regeneration and creativity, while the diaphragm lock (uddiyana bhanda) allows the energy to flow up from the lower abdomen area, enhancing the characteristic of patience and compassion within us. Where by the neck lock (Jalandhana bhanda) improves our endocrine function, manage our blood pressure well.
One can use bhandas with pranayama, asana and meditative practice with the guidance of yoga teacher to start off with. Once familiar with it, we can do it at different pocket of time we have in the day to experience their effects.