Cannot add music and sound effect to Timeline.

Running OSX 10.9.5 on MacBook Pro. iMovie 11 v9.0.9

No matter what I've done I cannot get two audio tracks under my video track. One track needs to be the music, the other track the sound effect. Have researched online and all I could find is something about a Content Library being the key to getting these two tracks in place. Can not find this mysterious "Content Library." l am going to add a shot of my iMovie project as it looks now . As can be seen, I can get both the sound effect and the music loop into the Timeline, but not one under the other. . . . .only side by side.

I sure hope someone can help. I've worked at this one detail for several hours now.

Any help appreciated.

Pat