Right away!
Ninjas are people that use abilities in order to perform missions, jobs, and other tasks. Ninjas are recognized by their use of chakra, the natural energy found in everyone, to utilize techniques and abilities. Ninjas may be part of a village, or disbanded and recognized as a missing-nin. There are different statuses for ninja ranks, which are generally ranked from Genin to Chuunin to Jounin to Kage. There are other groups of ninjas that make up different ranks, such as Anbu, which are a special task force. The main criteria that differentiates ninja from samurai is that ninja may utilize ninjutsu and genjutsu, whilst samurais only use kenjutsu and taijutsu in their fighting.
Chakra is the fundamental life force necessary to perform even the most basic tasks. As said previously, chakra is split into two groups, physical and spiritual energy. Balancing the two are what allows for proper execution of techniques. If someone has proper chakra control, when they activate a technique, it should not take so much chakra for them to perform a jutsu. However, someone with poor chakra control would use excessive chakra for techniques and run out of chakra faster. Additionally, there is a third part to chakra. For those who are capable of utilizing nature energy or senjutsu chakra, they also utilize nature energy alongside physical and spiritual energy. Doing so requires and incredible amount of chakra control and also a sizable chakra pool.
The 3 major fields of ninja techniques are taijutsu, genjutsu, and ninjutsu. Taijutsu is the simplest form of the there techniques. This revolves around the physical abilities of the user and fighting in close combat. Generally, taijutsu does not use any chakra, though chakra may be added to augment speed and strength. Genjutsu is another field. In this field, genjutsu revolves around casting illusions to others by disrupting their flow of chakra to affect them and place them in a false reality. In order to dispel a genjutsu, one must first disrupt their own chakra, or have another person do so. Another way would be to physically damage yourself in order to escape the genjutsu. Finally, the most common technique is ninjutsu. Ninjutsu revolves around the user utilizing chakra to form techniques. The techniques vary from weak to strong, offensive to defensive to supplementary, and more.
Chakra can be molded into two categories, shape and nature transformation. Shape transformation revolves around changing the structure of the raw chakra in an attack. The strongest example of shape manipulation is the Rasengan. The counterpart to shape manipulation is nature transformation which revolves around changing the chakra into elemental natures. Nature transformation generally takes more control and is more energy consuming. Also, it is incredibly difficult to balance high degrees of shape transformation with nature transformation. So techniques that utilizes both transformations would be Chidori which has less shape transformation than the Rasengan, but added with nature transformation. Every individual has a natural nature element that they are inclined to use. In order to figure out this nature, there are specially made chakra papers that react differently depending on the user. Whatever varying outcome happens to the paper shows what nature a user is inclined to utilize. It is possible for more advanced users to learn more elements than one. There are also special KKG users that can mould two natures to perform an entirely new one. These natures cannot be taught however, and can only occur from genetic traits.
And that should be everything =D