When you first switch into the audio view of a script, the audio files are laid out end-to-end, using the length of the default option as the guide. As you move the mouse over each audio file, the cursor changes to the move icon and you can drag each audio clip left and right in time.
As you move audio, the audio to the right of the one you are moving will move relative to the previous item in the script. Given that you can move items before or after each other by dragging left and right, it is the order in the script (not the timeline) that dictates the relative positioning.
To check what is relative to what, click and start a drag on one item. All of the descending items relative to that item will move.
Relative positioning is useful to keep the flow of sentences sounding natural even when there are differences in length between the elements.
As the screenshot below shows, the "Here in London" clip is unlocked, so if the "Its another monday afternoon" clip plays before it, it will move back in time, to keep the gap between the two clips the same.
Absolute positioning will fix that audio item to that exact point on the timeline, irrespective of what has happened before it.
The illustration below shows the "Here in London" clip again, but now it is locked so the gap between this and the previous item will contract.
This is really useful when you need audio to match to the beat of music, or perhaps a tag line at the end of an ad that always hits the 30s mark.