Meaning: This sentence describes the way songs move through the air in the morning. It's like saying,
Choice of Words: "Songs" are pieces of music. "Float" means to move smoothly and easily through the air or water. "Sweetly" means in a pleasant or enjoyable way. "Morning air" is the air in the morning. When you put it together, it means pieces of music move smoothly and easily through the air in the morning in a pleasant or enjoyable way.