If you tried inserting an audio clip into your iMovie project and found that it became the background soundtrack for the whole project, so you couldn’t reposition it or apply audio adjustments, then this tip will show you how to fix that problem.
When you drag an audio clip from the Music browser into your project, DO NOT LET GO while the background of the project is green.
Instead, move the clip over the segment of video where you want the audio to start, until you see a green vertical line and plus sign (instead of the green background).
Then you can release it and it’ll appear as a small ribbon under the video. You can click and drag to reposition the audio clip or use the dropdown to access the audio adjustments.
This process is a bit difficult to capture in screenshots, so here’s a short video that illustrates it: