If introduces conditional sentences that can express real or unreal situations. Real conditional sentences use the present tense or present perfect to discuss possible future events, such as "If it rains, we'll stay home." Unreal conditional sentences use past tense forms like "would" to discuss improbable or impossible events in the present or future, such as "You would understand me better if you came from my country." The document provides examples of conditional sentences for both real and unreal situations.