The original question had to be edited. I would suggest that one way in which Steinbeck conveys theme is by displaying it through different characters. For example, the theme of dreams and "the American Dream" is seen in Lennie and George, Candy, Curley's wife, and Crooks. In being able to show this theme in the words and thoughts of different characters, Steinbeck has been able to convey its significance. In each setting, the theme is the same, almost uniting the characters and creating solidarity between them, even if they don't know it. In this way, Steinbeck is able to convey theme.
Another way that Steinbeck is able to convey theme is through situations in which the theme is evident. The theme of idealism and reality is shown in different situations that makes it evident. When Candy sees Curley's wife's dead body, he recites his dream, almost as if in that instant and situation, the theme demonstrates itself. This is the same experience that Lennie and George share at the end in which both talk about their dream as George is about to shoot Lennie. In each example, the situation helps to convey the theme.