He says that Lennie was kicked in the head by a horse and that he was George's cousin.
To not say anything to the boss and if they get in trouble to go back to the camping spot
George told his new boss that he and Lennie were cousins and that Lennie was kicked in the head by a horse when he was a child, which affected his mental capacity. George also said they travel together because Lennie is a good worker but not very smart, so George looks after him.
Slim saves George and Lennie's jobs by talking to the boss and vouching for them, emphasizing how hard they work and how valuable they are to the ranch. He convinces the boss that George and Lennie are good workers who deserve to stay on despite the trouble they accidentally caused.
He lied to the man, he said the job was done, but what really happened was that Lennie got them kicked out of Weed
He's afriad that they would lose their job if The Boss knew about Lennie. The Boss would think Lennie would be some useless person that he's paying for nothing. That is why George emphasizes on how strong he is, because Lennie is very strong. And would be helpful to work. George had said they were cousins because The Boss was thinking that George had been bringing Lennie around to jobs, secretly stealing Lennie's money; Tricking his older bosses. Though George would never do this; He needed Lennie and Lennie needed him.
Shared misery and loneliness. Possibly even to have some kind of control of something in his poverty stricken life. It is one of the themes of the whole book. -- Lennie's Aunt told George right before she died to take care of Lennie. It was obligation for George.
Due to Lennies mental state, George tell the boss that he gets kicked in the head by a horse but evidentially the readers know that it didn't happen but for George to achieve his American Dream he'll do or say anything and later on in the novel we understand that.
GEORGE killed LENNIE because Curley was going to find him and shoot him anyway. George wanted Lennie's last few moments to be happy, so he decided to do it himself and tell him a story beforehand.
George tells the other ranch workers that Lennie stole the gun and accidentally shot himself while trying to escape. He does this to protect Lennie's innocence and spare him from facing a violent death at the hands of Curley and his men.
George tells Lennie to fight back and defend himself if Curley hits him. George wants Lennie to stand up for himself and not allow others to take advantage of him.
Carlson asks if Lennie had his gun and if George took it from him and killed Lennie. George responds, "Yeah. He had your gun...Yeah. Tha's how."
In the opening dialogue between George and Lennie in John Steinbeck's "Of Mice and Men," Lennie's forgetfulness, childlike nature, and dependence on George are hinted at through his repeated requests for George to tell him about their dream of owning a ranch. George's protective and authoritative tone towards Lennie also suggests a dynamic where George takes on a caretaking role for Lennie.