sasuke gets up as his sensei has arrived and bows down to him
alright sensei. I'll try to explain as good & clear as possible. Sharingan is dojutsu kekkei genkai, which appears in some members of the uchiha clan.literally meaning "copy wheel eye", it is said to be one of 3 greatest doujutsu, along Rinnegan and byakugan. It first manifested in Indra, the earliest ancestor of the uchiha clan and the elder son of Rikudou Sennin.
The abilities of Sharingan
The "Eye of Insight" ability makes the user able to see chakra flow. The sharingan itself gives colour to chakra, allowing the wielder to differentiate them. They are also able to tell if a person is under a genjutsu because the person's chakra flow would be irregular.
While for the "Eye of Hypnotism" ability, it grants the user an incredible clarity of perception, allowing them to easily recognize genjutsu and different forms of chakra. This also allows the user to pick up on subtle details, enabling them to read lip movements or mimic something like pencil movements.
The Sharingan's third and most well-known ability is that it grants the user the ability to copy almost any technique that he or she witnesses, apart from other kekkei genkai techniques. The user can memorise ninjutsu, genjutsu, and taijutsu with near-perfect accuracy, allowing the user to use the techniques as their own, or even modify them to create their own new techniques.
The Sharingan's fourth ability is capable of inducing a unique brand of hypnosis that involves suggesting actions and thoughts to the opponent through genjutsu cast by simple eye contact between both parties. iMore advanced Sharingan users can take the hypnosis ability even further to the point where a powerful summon or even a tailed beast (Bijuu) may be controlled.
1tomoe
Sharingan's first stage is the one tomoe. Upon the awakening of sharingan, the eye usually gains one tomoe first. While the doujutsu is active, it will grant the user some abilities such allowing the user to track movements and speed, allowing the person to see chakra and be able to react at the best time possible against and attack, and allowing to see through D-rank genjutsu.
2tomoe
Sharingan's second stage is 2 tomoe. The 2 tomoe Sharingan grants the user some abilities, such as motion perception better than the previous stage and the ability to copy movements nearly flawlessly, being able to track faster movements, probably twice faster than those seen by 1 tomoe rinnegan, being able to read hand-seals and predict the ninjutsu triggered of it, and the ability to see through & break C-Rank Genjutsu.
3 tomoe
Sharingan's third stage is 3tomoe. the 3 tomoe sharingan grants the user some abilities, such as being able to perceive and copy movements such as taijutsu, hand-seals of opponent flawlessly and nearly perfect and of course can use the same technique as them, being able to keep up with really high speeds, being able to see through and break B-Rank Genjutsu, and ability to hypnotize the enemy or in short, put them under genjutsu, by making eye contact with the enemy.
Mangekyou Sharingan
The next stage of sharingan is called Mangekyou Sharingan. this is indeed much more powerful than the previous stages. it is awakened through the trauma experienced from the death of a person very close to the Sharingan user. To obtain the it, one must feel the emotion of losing a friend or family. It is distinguished from a normal Sharingan by its appearance, which changes the form of the tomoe seal. Unlike the Sharingan, the appearance of the Mangekyō Sharingan differs from user to user. Mangekyou sharingan grants the user new abilities. for example, amaterasu, tsukuyomi, and for those who have both mangekyou, they could awaken susanoo. there are also special techniques such as kamui, and enton: Kagutsuchi. but if one keeps using the mangekyou, sooner or later the eyes will get blind.
Eternal Mangekyou Sharingan
This is the highest and most powerful stage of sharingan. so far, only Madara Uchiha and Sasuke Uchiha to have awakened EMS. To awaken these eyes, one needs to be transplanting another pair of Mangekyō Sharingan from a close relative, such as a sibling. this is also done to prevent the user from losing lights of the eyes after overusing Mangekyou Sharingan.