Candy is telling Lennie and George that he hurt his arm.
From the text:
Candy said, “I ain’t much good with on’y one hand. I lost my hand right here on this ranch. That’s why they give me a job swampin’. An’ they give me two hunderd an’ fifty dollars ‘cause I los’ my hand. An’ I got fifty more saved up right in the bank, right now. Tha’s three hunderd, and I got fifty more comin’ the end a the month.
The farm is important to Candy because he has nowhere to go when his time at the ranch is over. He wants a home, a future, somewhere that he can contribute. The pace George is talking about would give him companions and a way to spend his time..... a way to be useful.
Of Mice and Men
