Examples of direct characterization in Of Mice and Men.

Direct characterization is a literary device. A literary device is a format or structure used by authors to add more meaning, description, or uniqueness to the typical words that are used in writing.
Direct characterization consists of describing a character both inside and out. This gives the reader a clear picture of what the character looks like, and sometimes it could provide us with information about the character's personality traits. Direct characterization can come from the narrator or from another character who describes themselves or other characters outright—or "directly."
In Steinbeck's Of Mice and Men, we find direct characterization as early as chapter 1 when the narrator describes the two main characters. In this particular novel, direct characterization serves several purposes aside from illustrating the characters. The first is to accentuate how physically different and contrasting these two characters are from one another. The second is to show how their physical traits are dissonant with their personalities.
For example, the men are described in the following way:

Both were dressed in denim trousers and in denim coats with brass buttons. Both wore black, shapeless hats and both carried tight blanket rolls slung over their shoulders.

George is described with special emphasis on his small size and strong hands:

The first man was small and quick, dark of face, with restless eyes and sharp, strong features. Every part of him was defined: small, strong hands, slender arms, a thin and bony nose.

The author then moves on to Lennie, who is described as George's "opposite:"

Behind him walked his opposite, a huge man, shapeless of face, with large, pale eyes, and wide, sloping shoulders; and he walked heavily, dragging his feet a little . . . His arms did not swing at his sides, but hung loosely.

We can immediately tell that the narrator wants to emphasize the "sloping," "loose" way that this "huge" man's limbs hang in comparison to George's "small but strong" arms. There, we can tell that size does not matter when it comes to who is the dominant male in this relationship. All this is possible thanks to direct characterization. 
https://literarydevices.net/direct-characterization/