What are two reasons why George wants Candy to stall before telling the other ranchers in Of Mice and Men?

When Candy shows George the dead body of Curley's wife, George's initial reaction is to "tell the guys" so that they can put Lennie behind bars. He tries "to reassure himself" that maybe Lennie will be treated mercifully behind bars. However, Candy says that they should give Lennie a chance to "get away" because Curley will "wanta get 'im lynched." George understands that this is, in fact, what will happen to Lennie if he is caught.
George then asks Candy to wait for a few minutes before leaving the barn to announce the death of Curley's wife. George doesn't want to be the one who tells them in case they think that he "was in on it," so he asks Candy to stall so that he, George, can get away. He says that he will then come back into the barn with the other men and pretend that he is seeing the dead body for the first time. The men then won't think that George had anything to do with the death because he will appear to be seeing the body for the first time. The men also won't think, as they might otherwise think, that George has had time to help Lennie get away.
By drawing the attention away from George in this way, Candy will also be giving George the opportunity to find Lennie first. The rest of the men won't insist that he stays with them, because they won't suspect him of having had anything to do with the death. This will give George the opportunity of dealing with Lennie more kindly and more mercifully than would otherwise be the case.

Lennie has just inadvertently killed Curley's wife. George realizes that his friend is in serious danger and need to be protected. When Candy comes into the barn and sees the dead body of Curley's wife lying on the straw his immediate reaction is to ask George if "it's all off," meaning their plan to operate their own ranch.
George doesn't answer directly; the ranch is the last thing he's thinking of at this moment in time. His first priority is to protect both Lennie and himself. So he wants Candy to help him out by waiting for a minute after George goes to the bunkhouse and then coming in and telling everyone that Curley's wife is dead. This way he hopes that he can somehow protect Lennie from what's about to happen and make it look like he—George—had nothing to do with the killing.