The Sharingan is a bloodline limit passed down the Uchiha clan it allows users to copy any technique viewed buy it. The Sharingan has three primary stages you can tell what stage of development the Sharingan is at by the number of commas in each eye.
The first stage of the Sharingan Allows users to copy Ninjutsu and Taijutsu perfectly.
The second Sharingan stage allows people to copy and dispel Genjutsu.
Once the Sharingan becomes fully activated the user can predict an enemy's attack buy there brief twitching of their muscles.
The Mangekyou Sharingan is a heightened form of Sharingan. The Mangekyou Sharingan is distinguished from a normal Sharingan through its appearance, which changes the form of the tomoe seal and grants the user new abilities which also vary from person to person.
abilities are The first is Tsukuyomi, a powerful genjutsu. This jutsu comes out of and puts strain on the left eye. Upon making eye contact with an opponent, Itachi can use Tsukuyomi to transport them to an illusionary world where days amount to a mere moment in reality. Because Itachi is in total control of this world, he can torture an opponent in any way imaginable, leaving them crippled and in a state of mental collapse, though he hasn't gone further than 3 days. The second jutsu is Amaterasu. This jutsu puts strain on the right eye, and caused his eye to bleed during his final fight with Sasuke. Described by Zetsu as the ultimate ninjutsu, it is shown to be capable of burning through almost anything by creating a jet-black flame said to be as hot as the sun and capable of burning for seven days and seven nights.
The final and most powerful of these jutsu is the devastating Susanoo Jutsu. The jutsu summons a massive ethereal warrior, which then fights on behalf of Itachi. In the left hand, the warrior wields Yata No Kagami, a shield that's capable of reflecting all attacks, and in its right, the legendary Totsuka no Tsurugi also known as the Sakenagi Longsword . The Totsuka no Tsurugi, commonly sheathed in a sake jar held by a third hand growing from Susanoo's right forearm, is an ethereal weapon with an enchanted blade capable of sealing anything it pierces in an eternal dream-like illusion.
Kakashi Hatake developed his own version of the Mangekyo Sharingan during the timeskip. Kakashi uses his to create a localized interdimensional space-time warp, allowing him to target any object and send it to another dimension. The attack requires considerable effort to aim precisely and appears to leave Kakashi's chakra significantly drained; he collapses after using the technique three times in a single day (compared to his other original move, Lightning Blade, which he can use four times a day).
Sasuke Uciha has all the same abilities as his brother
Eternal Mangekyo Sharingan
If one Uchiha member who had awakened their Mangekyo Sharingan then took the eyes of another who had performed the same feat they would unlock the Eternal Mangekyou Sharingan. Taking the look of both users' Mangekyou eyes, it doesn't have the weakness of going blind with time and usage.
The man who discovered this and is currently the only person to do so is
Madara Uchiha who took his brother's eyes.
Madara and Izuna awakened their Mangekyou's around the same time due to their rivalry.
What Madara can now do with the EMS is currently unknown, it is speculated that he may possess all the Mangekyou abilities displayed by Itachi, Kakashi and Sasuke.
It may also explain his apparent immortality. All that Madara has said about it is that it is flawless and contrary to speculation, Izuna willingly gave him his own eyes.
Although this remains to be proven and Madara is known in the series for not telling the entire truth on certain subjects.