Chakra is the moulding of physical energy in every cell and the spiritual energy from the mind. Chakra can be controlled by using hand seals, making things such as walking on water, breathing fire, and creating illusions possible. Most ninja have one affinity to the five types of chakra. There are five basic types, stronger and weaker to one another. Their weaknesses and strengths are known to every shinobi. There is also Yin and Yang which is the balance of mental and physical energy. Kekkei genkais cen be formed by mixing two elements. Kekkei Tota can be formed by mixing three elements. Though many ninja can use many types of chakra, few can use them simultaneously. Chakra also seems to reflect a person's personality, as Karin said Sasuke's chakra grew darker when fighting Danzo.
Chakra is said to be from the Hagoromo, the Sage of the Six Paths. But, Hagoromo was only born with chakra from his mother, Kaguya. who in turn got chakra by eating the fruit of the Shinju. Kaguya ended the wars with her chakra. Hagoromo created Ninshu. which made people understand each other without talking. Instead, people used it to create ninjutsu.
Shinobi, or called Ninja, are the main focus of the series. A female shinobi is called a Kunoichi. They come from a hidden village, some from a clan, and they perform missions for a fee. This missions include; doing manual labour, acting as escorts, gathering secret information, retrieving stolen items, carrying out assassinations, etc. In war, ninja go together to defend their village and land. Ninja are expected to be loyal to their village all of their life, so every ninja who leaves are called missing-nin and to be marked to death. Ninjas mould their chakra to use jutsu. Shinobi may have one affinity of the five types. This can be determined by using a special kind of paper. When the paper cramples, you have a lightning affinity. When the paper slices in half, you have wind affinity. When the paper damps wer, you have a water affinity. When the paper burns, you have a fire affinity. When the paper turns to dirt, you have an earth affinity.
Ninjutsu refers to almost every technique which allows a person to do something they otherwise can't be doing. The effects of ninjutsu are real unlike genjutsu. Complex ninjutsu allow shinobi to perform healing, nature transformation, etc. Almost all ninjutsu requires hand seals to be performed. Basic ninjutsu are one of the five basic elements while advanced ninjutsu requires two or more of them combined. There are two methods in manipulating chakra; 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. Ninjutsu can be used with Taijutsu to create nintaijutsu techniques