How many times have you felt that two of your favourite teachers are as different as night and day? One is so outgoing and the other is so soft spoken, but both are excellent teachers. When you used the stark difference between night and day to describe the difference between two of your teachers you were making use of a figure of speech in English called a SIMILE.
Similes help to drive home a point forcefully when two disparate things are linked with a common feature between them. Similes make use of the words AS and LIKE to establish the common feature. Similes are among the many figures of speech used by writers and speakers to express themselves very clearly and in a colourful way.