First of all, it should be noted that the length of the audio cannot exceed the length of the entire video project.

When you find a suitable audio/music clip, check its duration.

Then, add a scene, and adjust the scene's duration according to the audio clip.

Finally, add this audio to the timeline.

If you've already added audio to the timeline but it doesn't show the complete clip, you need to drag the edge of the video/image track to lengthen the scene duration first.