While the word chakra, often translated at “wheel” or “circle,” can be found in the Vedas (which date from 1000 to 1500 BCE), these embodied psychic energy centers arguably didn’t get defined until the eighth century CE, when a few Buddhist texts describe a three-chakra system. The notion of a chakra system really gains steam a few hundred years later, in the age of hatha yoga and Tantra.
Depending on the text, a variety of different numbers of chakras are given. I have had teachers who have referred to hundreds of chakras in the body, explaining that each and every joint is a chakra. Most commonly today teachers illuminate and refer to the seven main chakras that can be found or experienced along our central channel, or Sushumna Nadi.
The chakras are correlated with the five elements, which will then have a correlation to a bija mantra (seed sound), which was originally used in a practice called nyasa. From the word meaning “to place,” nyasa involved visualizing sounds and shapes and mentally placing them at different centers of the body. Perhaps you can think of each chakra as being like a special folder on your computer and the mantras as different ways to double click on that folder in order to open up the multitudes of information that it holds.