I wish I could fly.

Meaning: This means that the person speaking wants to be able to fly. It's like saying, I want to be able to move through the air like a bird.

Choice of Words: I is a pronoun that means the person speaking. Wish is a verb that means to desire or hope for something. I is a pronoun that means the person speaking. Could is a modal verb that means to be able to do something. Fly is a verb that means to move through the air using wings. When you put them together, "I wish I could fly" means that the person speaking desires or hopes to be able to move through the air using wings.