Oscar Wilde's The Importance of Being Earnest is a satire, or a comedy of manners that pokes fun at and critiques the mannerisms and values of the upper class. Wilde incorporates a number of comedic techniques to highlight the targets of his satire. Three of these include hyperbole, verbal irony, and dramatic irony.
Hyperbole is a figure of speech that exaggerates for comedic effect. Wilde uses this device frequently in the play, as the characters exaggerate the importance of trivial things. For example, Algernon tells Jack that "Gwendolen is devoted to bread and butter" in act 1. This is hyperbolic because "devotion" is much too strong a term to describe someone's preference for the relatively plain bread and butter.
Verbal irony is irony at the sentence level, in the word choice. The author or character says the opposite of what is meant. When Algernon tells Jack that he must be named Ernest because he is "the most earnest looking person I ever saw in my life," this is an example of irony because the adjective "earnest" means honest or sincere, and in saying his name is the sound-alike "Ernest," Jack is actually lying about his name.
Dramatic irony is irony that occurs when a character does or says something on stage that indicates that the character does not know something the audience knows. For example, in act 2, Gwendolen and Cecily think they are both married to "Ernest," unaware that both Jack and Algy are lying about their names—that there is actually no Ernest at all.
These are just a few of many examples, all of which work toward Wilde's satire of the upper class.