If you are referring to John Steinbeck's introduction of his main characters in Of Mice and Men, I assume you are looking at how the author describes the men physically at the book's outset.
In a sense, he allows the men to begin on an "equal footing:" Steinbeck relates how they are similar. Both are wearing...
denim trousers...denim coats with brass buttons...both wore black, shapeless hats...and both carried tight blanket rolls...
This is where the similarities end, for indeed the men seem to be complete opposites.
The man we learn to be George is small in stature, but everything about him is purposeful and focused:
quick...restless eyes...sharp, strong features. Every part of him was defined: small, strong hands, slender arms, a thin boney nose. Behind him walked his opposite.
Lennie is very different from George:
...a huge man, shapeless of face, with large, pale eyes, with wide, sloping shoulders; and he walked heavily, dragging his feet a little...His arms did not swing at his sides, but hung loosely.
By comparison, we find that George is sharp in every aspect: his looks, his movements, etc. He is small, but precise and well-defined in appearance.
Whereas Lennie has a shapeless face, perhaps even body. His movements are slow and dragging.
While George is aware of everything, calculating and quick with regard to what lies ahead, Lennie is passive. George is a leader—mentally alert; Lennie is a follower—impulsive and "slow" in many ways.