Situational irony is when the outcome of a situation is different from what was expected. For example, a student who studies hard for a test but fails may experience situational irony.
Dramatic irony is when the audience knows something that the characters in a story do not. For example, in a play, the audience may know that a character is about to be killed, but the character does not.
Verbal irony is when someone says something that means the opposite of what they intend to say. For example, a person may say "It's a nice day outside" when it is actually raining.