Adjusting music adding to iMovie

You will see a thin horizontal line going along the middle of the audio clip.

Hover your cursor over it and drag it down to reduce the volume.

Dragging it up will increase the volume.

As I understand it you have some video clips with talking and have added a background music clip underneath, the volume of which you want to lower so that it doesn't drown out the talking.

Ian's way of dragging downward the horizontal volume adjustment line in the audio clip would work. If you want to lower the volume of just the portion of the audio clip that is beneath the video clip there are a couple of ways of doing that.

The first way is to select the video clip and then click on the loudspeaker icon in the tool bar at the upper right of your screen. A box will appear that has the language "lower volume of other clips". Check that box and it will lower the volume of only the portion of the audio clip that is beneath the video clip. Wherever you move the video clip, the volume of the audio clip beneath it will be lower for the duration of the video clip.

Here's another way to lower the volume of just a portion of an audio clip. While holding down the r key, press-drag your cursor over the audio clip where you want to lower the volume. As you drag, a yellow box will appear to outline the range where you want to lower the volume. Drag down the horizontal volume adjustment line within the yellow box to lower the volume only of the audio portion outlined by the box.

-- Rich