Chakra is an energy which is present in every living being. It is created in a special organ called the Chakra coils in humans.
Chakra is produced by molding of Physical and Spiritual energies together. Where Physical energy is the energy produced by the physical strength of the body, and spiritual energy is produced by mental strength of brain.
The chakra circulated throughout the body in a network called the 'Chakra Pathway System', which was similar to cardiovascular system but instead of blood, chakra runs in it. Certain people could generate chakra naturally or learn to generate chakra and release it outside their bodies through the chakra pressure points called 'Tenketsu' to use various jutsus.
Tenketsus were extremely tiny nodes which lied along ones chakra pathways, There were a total of 361 tenketsu in a human body. Along with the Eight inner gates which restricted the overall movement of chakra, tenketsu controlled the flow of chakra in ones pathways. They were a way to control the chakra in the body, if there were no inner gates and tenketsus, people would explode to death as soon as they access chakra.
Chakra is divided in four types.
1) Normal Chakra : Used by everyone on the planet, seen as Blue in colour if we see it through Byakugan or Sharringan.
2) Beast Chakra : Used by different kind of beasts throughout the world. It is usually corruptive in nature, but can be purified through the use of Nature energy. seen green and yellow in clour.
3) Tailed Beast Chakra : As the name suggests, it is chakra of tailed beasts. It is Highly corruptive in nature and can drive people to madness. Jinchurikis posses this chakra, though it can controlled with the help of tailed beasts.
4) Sage Chakra : It is chakra infused with nature energy, gives any kind of chakra a qualitative upgrade. Nature energy gives a huge boost to Strength, agility, defense, endurance and regeneration.