What a Sharingan is: A doujutsu in the world of Naruto and the RP. It is considered to be the middle in terms of power amongst the three doujutsus, Byakugan, Sharingan, and Rinnegan. The Sharingan is wielded by Uchiha members, however, not all of them are fortunate enough to gain the Sharingan. To first activate the first tomoe the user must experience a life threatening experience that made hatred grow inside their body. That is the first stage and the farther stages are obtained by practicing the use of Sharingan and getting more experience with it. That applied to the second and third tomoe. The next level aftertthe third tomoe is the mangyekyo Sharingan, and even Eternal Mangyekyo Sharingan. To unlock the MS, an Uchiha has to 'kill their bestfriend' and to obtain EMS, an Uchiha has to transplant another MS from another Uchiha.
Users of the Sharingan: Some known users include Madara Uchiha, Sasuje Uchiha (EMS), Shisui Uchiha, Izuna Uchiha, Itatchi Uchiha, Obito Uchiha (MS) Two non Uchihas have the sharingan as well, Hatake Kakashi and Danzo. They obtain the MS by transplanting it from Shisui Uchiha and Obito Uchiha. However, they are limited to only one Sharingan eyes and therefore, limited in abilities.
How Each stage differs: Simply put, the main difference is the appearance of the Sharingan and the extent of their visual prowess, which includes genjutsu and tracking quick movements.
1T Sharingan: The ability to see chakra within a shinobi's body. The 1T sharingan allows the wielder to see through illusions D-rank or lower. They will also be able to track movement speeds by others even faster then themselves and follow taijutsu moves by other shinobis. The eyes will look bloody red with one tomoe surrounding the pupil.
2T Sharingan: After the 2nd training session, the wielder of the Sharingan will gain a second tomoe in their sharingan. They will have the ability to see through illusions C-rank or lower. Theyre ability to track movement speeds higher then themselves will be enhanced as well as taijutsu. In addition, they will be able to anticipate movement by analyzing higher speeds and by reading handseals, anticipate and 'copy' the targets techniques.
3T Sharingan: After the third training session, the wielder of the 3T sharingan will have enhanced genjutsu abilities (RP), they will learn more illusions that reflect the visual powers of Sharingan. In addition to its illusion, the wielder of the 3T will be able to track movement speeds higher then theirs and taijutsu as well. Of course, the level in which they track will be much greater then the previous tomoe. They will also be able to anticipate the techniques their opponents use by analyzing the handseals their opponent uses. (Of course you'd need to know the technique itself.) The blood red eyes will gain a third tomoe.
MS: Basically, the wielder of the MS will get increased tracking abilities and anticipating movements. They will also be able to perform forbidden techniques only known to mangyekyo users. This includes ameterasu, Susano'o (if you have two) and more forbidden techniques. (Like Izanagi, I think.) However, they will take damage everytime they use their Mangyekyo Sharingan. Their blood red eyes will somewhat merge their three tomoes to form a cool design.
EMS: The user will gain even higher tracking abilities then the previous level and also will be able to analyze and anticipate the opponents moves. They won't take recoil when using the Eternal Mangyekyo Sharingan and their blood red eyes gets an even cooler design then the previous MS. The wielder will be able to perform Susano'o, the last and complete version of Susano'o. Some characters can manipulate the Ameterasu, like Sasuke Uchiha.
How the Sharingan is used: What these have in common and their difference: Simply put, each and every level of the Sharingan can see chakra in a shonobi's body, but the higher the level, the better you can see chakra. This includes later versions of the Sharingan, where the 1T can see chakra points of the body while the later versions can see through walls to check the chakra points. Each level can track movements and anticipate techniques (1T excluded.) There abilties to anticipate, analyze, and track movements gets better as they level up their sharingan. 3T is where the user will be able to perform a new set of genjutsu in the RP and the level the sharingan user can see through Genjutsu progresses with the next level of Sharingan. MS and EMS unlocks abilities like Susano'o, Ameterasu, and Izanagi/Izanami (something like that.)
Uchiha Clan History: They are one of the two known direct descendents of the Sage, the Uchihas and the Senjus. The Uchihas are known for their visual powers and the Senjus are known for their strong life force and Chakra reserves. For years and years, the Uchiha continuously fought amongst one another to prove which is stronger then the other. This war was caused because they were known as the two strongest clan at that time. The Uchihas were filled with Barbaric, blood thirsty evil maniacs while the Senju's where more civilized and seeked peace. Hashirama and Madara were known to be the strongest from their clans, therefore they fought constantly. Hashirama soon made a peace treaty with Uchiha, where they all followed, all except Madara. Madara did not like the plan and left the village. He came back to fight Hashirama in the valley if the end and ended up losing. He went in hiding for the following years. at that time, another Uchiha prodigy was born, Itatchi Uchiha. By 13, the Konohagakure officials ordered him to slay the Uchiha clan, mainly because of the attack of the 9 tails where they suspected an Uchiha member took control of the beast. Itatchi did as he was told and killed all but one, Sasuke. He was soon classified as an S rank criminal despite the officials knowing the truth. Sasuke grows up and becomes strong, strong enough to kill itatchi. Okay, I'm getting off of track, lmao. Back to the nine tails attack, Obito Uchiha took the liberty to unseal the nine tails from its jinchuriki. He took control of it with his Sharingan and Destroyed, er almost destroyed the hidden leaf. (Ordered by Madara, I think.) So that's all, basically. The Uchihas are almost completely gone, all but Sasuke and Obito.
Here is everything i know, copied and pasted from my last training thread <.< as for my 1T experience, i awakened it at first then died due to a harsh beating then went back to life and grew hatred against my sensei after he beat me again and now i have 1T :3