It is best to start with an except of the dream itself, so that you can get a sense of what George and Lennie are talking about.
“O.K. Someday—we’re gonna get the jack together and we’re gonna have a little house and a couple of acres an’ a cow and some pigs and—"
“An’ live off the fatta the lan’,” Lennie shouted. “An’ have rabbits. Go on, George! Tell about what we’re gonna have in the garden and about the rabbits in the cages and about the rain in the winter and the stove, and how thick the cream is on the milk like you can hardly cut it. Tell about that, George.”
Based on this text, we can make a few observations.
First, George and Lennie do not want something grand. They just want something to call their own. For example, they only want a few acres of land, a few animals, and a garden. They want this, because they are migrant workers. This means that they do not have a place to call home. What they want is a home.
Second, George is the dreamer of this vision, as Lennie wants George to speak of it. So, George, as a good friend, complies and gives the dream over again. He probably did so many times already. Also the men will do it together. This is an important point, because friendships are rare in Steinbeck's world.
As for character, we can see that this dream speaks well of both George and Lennie. They are tired of wandering, working, and barely making it. What they value is the simple life and a place to call home. They also value friendship, as they are going to do this together.