The Sharingan is the pre-evolution of the legendary doujutsu known as the Rinnengan.
The sharingan can only be awaken by the members of the clan uchiha, it was 5 stages
Sharingan Tome 1 awakes by when the user is put in a hard dangerous situation like when sasuke were fighting haku.
Sharingan Tome 2 awakes by a even harder situation
Sharingan Tome 3 this is the master version of the sharingan, the user needs to be put un life and dead situation.
Also the sharingan has 2 stages above the normal sharingan, it is called mangekyu sharingan at legendary stage that only 5 members of the clan uchiha had archived it. ITachi,Shisui, Madara, izuna, Sasuke and there was one exception to the rule.. HAtake kakashi, to awake the mangkyu the user needs to feel the greve of the person most closer to him or killing ur bestfriend but the continous uses of the mangekyu makes the user go blind and unlock a new tecnique of the sharingan.
There is only one way to stop the blindness that will come after, it is only archived by transplating the eyes of a member of the clan uchiha (your brother) then you will archive the Eternal Mangekyu Sharingan. Only Uchiha Sasuke and Madara are known for that Archivement.
The sharingan has the ability to copy ninjutsu, Taijutsu.
Break genjutsu easly
see the collor of the chakra
Track highspeed moment.
With the Mankyu Sharingan the user may gain access to a new techniques like Tsukoyomi, Amataresu, Kumai or Susano.
Susano can be obtain if you gain Amataresu and Tsukoyomi