What's "if only" mean and when's it used?

Native speaker’s answer
Rebecca
Here, "if only" means "for the single purpose of;" for no other reason. It's used to state or emphasis the single reason for something. It can also be used to express a wish at the beginning of a statement, maybe with regret. Ex: I'll go if only for the snacks. Ex: If only I could fly to Spain to see her. => wish Ex: If only I had studied for my test. => regretful wish Ex: She goes home if only to see the dog