Back story
-The sharinganis a type of Kekkei Genkai and it originates from the Sage of Six Paths the god of shinobi. The unique kekkei genkai comes mainly from the Uchiha clan.
Abilities
-One of the main abilities the shairngan allows you to have is the ability to see the flow of chakra clearly.. Another big a ability the sharingan grants is clarity of perception.. allowing them to easily be able to recognize genjutsu along with numerous types of chakra. They can read simple movements like a ball bouncing. As the number of tomos increases the ability to perceive movement increases.. allowing the person to read even faster movements. The third most commonly known attribute of the sharingan is the ability to copy almost any jutsu.. just by seeing it while the sharingan is active. The user is able to memorize genjutsu,taijutsu, and ninjutsu and is able to do it perfectly. Though despite the sharingans ability to copy techniques.... the user is not always able to.. this can be because of numerous reasons such as.. the users limit.. an example would be when Sasuke copied Lee's taijutsu.. Though he was able to copy some of his moves.. Due to the limit and extent and overall lack of training Sasuke wasn't able to perform all of what Lee did. Another thing the sharingan cannot copy would be any kekkei genkai techniques and summonings.. Basically anything dependent on the user.