In Opus, each object you add to a page is automatically put on its own layer. Below is an illustration of one page in a publication:

The text object named Title is on the top layer, followed by the Score, Level 1, Timeline 1, Ship and Play Game objects.

If any of these objects overlapped, the object on the uppermost layer would appear above an object that is on a lower layer.

Layers can be important to give the appearance of depth. For example, if you animate an object, such as a plane flying through clouds, you may want to have the clouds appear above and below the planes layer, to give the appearance of it flying in front and behind the clouds.

Note: You can easily change the layer order by dragging objects up and down the list in the Objects tab of the Organiser.