There are various examples of irony throughout this play, in addition to the devices the previous educator has mentioned.
Verbal irony is when a speaker's words contrast with the literal or actual situation. When Nora realizes that Torvald has sent a letter to dismiss Krogstad, she is horrified, believing that this will surely expose her secret. Torvald tries to calm her by saying,
Come what will, you may be sure I shall have both courage and strength if they be needed. You will see I am man enough to take everything upon myself.
In fact, Torvald does not have the strength to "take everything upon himself," and when he finds that Nora's actions might harm his own reputation, he panics. He tells Nora,
You have ruined all my future. It is horrible to think of! I am in the power of an unscrupulous man; he can do what he likes with me, ask anything he likes of me, give me any orders he pleases—I dare not refuse.
Torvald proves to be quite a coward, not a man of courage. In yet another twist, Torvald is required to "take everything upon" himself when Nora leaves him and their children.
Dramatic irony occurs when the audience is aware of something that at least some of the characters in the work are not fully aware of. In act 1, Torvald calls Nora his little "spendthrift" and asks whether she has been "wasting" their money yet again. In actuality, Nora has been steadily stashing money so that she can secretly repay a loan; she illegally procured the money so that she could pay for Torvald's medical treatments without his knowledge.
Situational irony occurs when events in the play (or story) turn out quite different than what was expected. When Nora asks Torvald to help Mrs. Linde get a job at the bank, Krogstad actually gets fired. Because of this, Krogstad is quite upset and threatens to expose Nora's forgery and illegal loan. In trying to help Mrs. Linde, Nora actually puts herself in legal danger.