In the beginning...
Some of the earliest philosophical and metaphysical concepts of mankind originated within the Indian subcontinent. Over the millennia, the original yogis extensively practised self-reflection and meditation, and gradually exposed their experienced truths in scriptures known as the Vedas (this often translates as wisdom or information). It is not agreed upon consistently just how old the Vedas are, with scholars ageing them between 1 and 8 thousand years old, all written at a different time. These 4 sanskrit texts are composed mostly of hymns, and served as a very strong foundation to the Hindu culture you find today.
Over the years, many inspired schools of thought developed, all seeking to further describe the nature of reality, creation, science, the human body, religion and much more. 6 dominant schools came out in direct lineage to the Vedas, and many more schools of thought also emerged that were not in lineage. Most of these schools of thought (on both sides) hold something as their holy grail in human reality: a truth, self-realisation, knowing god, oneness, nirvana, enlightenment etc. This was the same state of being reached by Buddha and Jesus alike, revered and worshipped for thousands of years. If you are aware of 'The Yoga Sutras' by the ancient sage Patanjali, you will understand that this text is a step-by-step systematic approach to reaching the very same truth or self-realisation. Many of the schools of thought mentioned earlier, in particular Samkhya and Yoga, utilise this great sage's work directly in the ideas you study today in yoga classes.
In modern yoga philosophy however, its practically impossible to claim something as a pure lineage. Every single school has adapted and incorporated techniques of many others. Hatha yoga for example draws heavily on Samkyha, Yoga and Tantra, among a host of others. Hatha simply gives you another systematic approach leading in the direction of an enlightened state of mind.
In Hatha Yoga (which is a form of Tantra meaning that we align and marry qualities of male-female, shiva-shakti, yin-yang etc), we have a concept of all energy in the universe at some subtle, higher level being one. This is called Shakti in Trantra, and talks about the energy of the entire manifested universe before it fragments/separates into its individual forms. It does this in much the same way that white light separates into all the individual colours through a prism. To help conceptualise this idea, start by thinking about one end of this spectrum of Shakti as dense, heavy physical matter and another other as the light, barely perceivable ether. These differentiated energies come together in infinite combinations, to compose the manifest reality we call our universe.
Tantra says that there are 7 levels to this reality. The macrocosm consists of everything in the external world, and the microcosm consists of everything in your world. A fundamental law of this philosophy states that anything found in one must have a corresponding element found in the other. What is within is also without, and vice versa.
And so finally, that brings us to the chakras...