Similes are comparisons that use the word "like" or "as." One example of a sentence that includes a simile is the following:
Counting houses, shops, stores, sail lofts, and one great ship after another, home again after their voyaging, content as cows waiting to be milked.
Johnny is looking out at the harbor from his attic window as he awakens in the morning. He see the boats and quiet scene of Hancock's Wharf. Likening the rows of ships to cows waiting to be milked conveys both the large bulk of the ships and also the peace and quiet of the early morning scene.
Another example of a simile is as follows:
Soon she’d be saying it was just like having a preacher live with them to hear Johnny Tremain read Holy Writ.
This is what Johnny imagines the illiterate Mrs. Lapham saying to him as she listens agape to him reading from Leviticus. Johnny has a pleasant, rolling reading voice that Mrs. Lapham apparently in the past has compared to the voice of a preacher.
However, Mr. Lapham, a church deacon and master of the house, sees Johnny's pride in his skill as a reader and humiliates him by making him swear to walk more humbly. At the end of the chapter, Johnny is so angry he is likened to an angry tom cat. Although he is controlling himself, he is spoiling for a fight, just as a tom-cat might:
Johnny stalked out of the kitchen as stiff-legged as a fighting tom-cat.
In the simile below, Dusty, a younger apprentice, follows after Johnny:
Dusty, good and quiet as a mouse, followed him.
Dusty is compared to a mouse: this is actually a cliche, an overused comparison, but it does make a point about Dusty.
Finally, the following Bible verse quoted in chapter one uses a simile:
And I will break the pride of your power; and I will make your heaven as iron, and your earth as brass