Kakashi got his sharingan eye from a friend, a member of the Uchiha clan. Kakashi, Rin, Obito and Yondaime were on a mission, and Kakashi had become a jounin on his birthday so Yondaime made him mission leader and went off to help fight a part of some massive war. Then during the mission Rin got captured, but Kakashi did not want to go and get her (the reason for this is because his dad, the White Fang of Konoha, did the same thing and became a disgraced ninja and killed himself). Obito then went off to get Rin back since he has a similar attitude to that of Naruto, and as he fought the guy that captured Rin he awakened his Sharingan... then Kakashi comes around to join the fight ('cause Obito gave him a speech beforehand) and long story short they win the fight but the guy they were fighting (an Iwagakure shinobi named Kakko) did a rock slide move ("Doton: Iwayado Kuzushi", AKA "Earth Release: Rock Lodging Destruction") to take 'em out. Since Kakashi couldn't escape in time, Obito pushed him out of the way, but Obito then got caught under Rock slide.
With half of his body crushed (namely the right side) he pledged his awakened sharingan from his left eye to Kakashi, and Rin (a medical ninja) performed the transplant for him. Kakashi then goes to fight the idiot that killed Obito with his newly acquired Sharingan, and Chidori (AKA One Thousand Birds), a move he had just recently invented. So Kakko ends up having the honor of being the first person to be killed by Kakashi's Chidori. And now that is why Kakashi has a sharingan. Also, that is why his "2 bells test" highlights friendship and team work, as he felt if he had made it there earlier Obito wouldn't have died
With half of his body crushed (namely the right side) he pledged his awakened sharingan from his left eye to Kakashi, and Rin (a medical ninja) performed the transplant for him. Kakashi then goes to fight the idiot that killed Obito with his newly acquired Sharingan, and Chidori (AKA One Thousand Birds), a move he had just recently invented. So Kakko ends up having the honor of being the first person to be killed by Kakashi's Chidori. And now that is why Kakashi has a sharingan. Also, that is why his "2 bells test" highlights friendship and team work, as he felt if he had made it there earlier Obito wouldn't have died