The document discusses three types of "if only" sentences used to express wishes, regrets, and complaints. The three types are: 1) Using the simple past to express a present or future wish with sentences like "If only I had more money"; 2) Using the past perfect to express regret over past actions like "If only I had woken up early"; and 3) Using "would" to complain about present behaviors as in "If only you wouldn't lie all the time."