Overview
Chakra is the fundamental form of energy that all individuals possess which allow them to perform supernatural feats. Overtime, it has grown to become a necessary component of living. If one were to run out of chakra, they would subsequently lose their life. Chakra is unique to the individual, with each person known to have their own "color" of chakra. Sensors or Dojutsu users are able to see this "color" and recognize specific traits, such as the clan of the person. Chakra moves through humans in similar manner to other biological systems, with it's own network known as the "Chakra Pathway System". This network has chakra move through it, passing through Tenkentsu, or nodes where chakra can be released from. Shinobi have learned to release chakra outside of their bodies this way to perform jutsus.
Chakra is combination of physical and spiritual energies. Physical Energy (身体エネルギー | Shintai Enerugī) is collected from each and every one of the body's cells and can be increased through training, stimulants, and exercise. Spiritual Energy (精神エネルギー | Seishin Enerugī) is derived from the mind's consciousness and can be increased through studying, meditation, and experience. The more powerful each of these energies become, the more powerful chakra that will be created. As such, training both physically and mentally are necessary to improve the quality of chakra produced.
Chakra Control
Besides the quality of chakra, chakra control is another important factor in the overall quality of a technique. With poor chakra control, a shinobi may utilize too much chakra and tire faster or utilize too little chakra and ineffectively perform a technique. Hand seals are often used to manipulate chakra more easily, allowing shinobi to execute their techniques faster and more effectively. Shinobi who are extremely skilled at chakra control often specialise in genjutsu or become medical-nin.
Regarding Ninjutsu specifically, two methods of chakra control are utilized. These methods are Shape Transformation and Nature Transformation. The first involves manipulating the form, movement, and potency of chakra. The second involves manipulating the properties of chakra to mimic an element. Yin-Yang Nature Transformation is unique in that it changes the ratio of spiritual and physical energies within chakra.
Types of Chakra
Several variations of chakra exist. Besides each individual possessing a unique chakra, chakra can be categorized into a specific set of groups.
Raw Chakra
Raw Chakra is the natural chakra one posses and expels from their body. Comparatively, Raw Chakra is weaker than Elemental Chakra, Senjutsu Chakra, and Bijuu Chakra. However, when advanced Shape Transformation is applied to Raw Chakra, certain techniques can stand up to previously mentioned list. Examples of these include Rasegan or the Hyuga's Rotation technique.
Elemental Chakra
Elemental Chakra is the result of applying Nature Transformation to chakra (whether it be Raw, Senjutsu, or Bijuu). There are 5 Basic Elemental Natures — Fire | Wind | Lightning | Earth | Water — and each one possesses it's own characteristics. Elemental Chakra Natures can be combined to create completely new elements, though this ability is limited to KG users. Elemental Chakra is naturally stronger than it's Raw Chakra counterpart.
Senjutsu Chakra
Senjutsu Chakra is the result of adding Natural Energy (自然エネルギー, Shizen Enerugī) within the mix of Physical and Spiritual Energy. Whereas Physical and Spiritual Energy is dependent on the user to increase chakra, Natural Energy is dependent on the nature surrounding the user. When properly added into the mix, it increases the power of the user's chakra tremendously. Summoning Animals seem to posses knowledge of Senjutsu Chakra due to their connection with nature.
Bijuu Chakra
Bijuu Chakra are unique to the Bijuu, or Tailed Beasts. Their chakra is much more dense and powerful. Jinchuurikis are able to utilize the chakra of their Tailed Beast while in any of their respective Tailed Beast modes.