NINJUTSU

Ninjutsu (忍術; Literally meaning "Ninja Techniques"), is a term referring to almost any technique which allows the user to do something that they otherwise would be incapable of doing, including the usage of weapons. Unlike genjutsu, which makes the opponent see illusions, the effects of ninjutsu are real. They vary greatly in purpose, with the simpler ninjutsu serving such tasks as transforming the user or allowing them to evade attacks. These techniques are often second-nature for experienced shinobi, who can use them at will. More complex ninjutsu manipulate one's surroundings or utilise the elements, respectively serving such tasks as healing others or manipulating nature transformations.
Ninjutsu, most of the time, relies on chakra and hand seals to be effective. The hands are put in sequential positions that moulds and manipulates chakra in the necessary manner to perform a technique. This is not always needed, however, and some techniques become second nature to experienced ninja, after which they can perform them at will.

An example of shape and nature manipulation combined.

Additionally, there is the kind of technique that can be classified as a basic or advanced elemental technique, the basic type are techniques with specific elements (wind, water, fire, earth, or lightning), the advanced type combine two or three of the basics elements and creates a new one.
When creating a ninjutsu, the two methods of manipulating chakra are referred to as shape transformation and nature transformation:

• Shape transformation deals with controlling the form, movement, and potency of chakra.
• Nature transformation usually deals with changing the physical properties of chakra into an element.

These two methods can be implemented separately or together in order to create a ninjutsu.
It is said that the Sage of the Six Paths was the first to explain the mysteries of chakra, travelling throughout the world to spread his ideas and religion, the Ninshū (忍宗; Literally meaning "Shinobi Sect"). The teachings were meant to give people a better understanding of themselves, as well as others, and lead the world into an era of peace. However, as time wore on, ninshū would eventually come to be known as ninjutsu, a more weaponised version of the Sage's teachings.
It can be used in collaboration with taijutsu to create nintaijutsu techniques.