Nathaniel Hawthorne uses lots of figurative language in his writing, and we can find a number of similes in chapter 3 of The Scarlet Letter.
At the beginning of the chapter, a stranger arrives in town. Although Hawthorne calls him a stranger, there is a recognition between him and Hester. Hawthorne uses two similes when he describes how the stranger looks at Hester:
It was carelessly at first, like a man chiefly accustomed to look inward, and to whom external matters are of little value and import, unless they bear relation to something within his mind. Very soon, however, his look became keen and penetrative. A writhing horror twisted itself across his features, like a snake gliding swiftly over them, and making one little pause, with all its wreathed intervolutions in open sight. (Emphasis added)
A simile is a comparison using the words like or as. Hawthorne uses this literary device to help us understand how the stranger's look changes once he realizes who Hester is. At first, he cares little for her, but once he recognizes her, he becomes fearful. By comparing the movement to a snake, Hawthorne helps us visualize this. As we continue to read the book, we might understand more why Hawthorne chooses to compare this man to a snake.
Hawthorne also uses similes to describe other characters:
There he stood, with a border of grizzled locks beneath his skull-cap, while his grey eyes, accustomed to the shaded light of his study, were winking, like those of Hester's infant, in the unadulterated sunshine. He looked like the darkly engraved portraits which we see prefixed to old volumes of sermons, and had no more right than one of those portraits would have to step forth, as he now did, and meddle with a question of human guilt, passion, and anguish. (Emphasis added)
The above quote describes John Wilson as he begins the questioning of Hester. Hester, however, refuses to name the father of her child:
"I will not speak!" answered Hester, turning pale as death. (Emphasis added)
Hawthorne uses a simile here to describe to us what Hester looks like, and by choosing to compare her to death, he also set the mood of the piece.