Layers are a list of the panels used in the design of your page.
If you are using the layout library to create your version, you can view the layers and right click to edit the content of the panel. It is also possible to lock layers and sometimes hide them.
However, if you are using a blank design or editable template, this palette is helpful for understanding the structure of your page and selecting panels that may be obstructed by panels higher up in the order.
You can select and drag a layer to move its position or right click to choose the arrangement (for example - Send to Back).
You can also right click on a layer to edit the name, copy/paste the settings or delete it.