The Layer system can be found at the left-end side of the Content Builder.
It has been designed to help you move elements around, group them in files and apply conditions.
Click on the Eye to hide/display an element.
Drag elements to make them appear in the front or in the back (top of the list are the forefront elements).
Use the three icons to duplicate an element, create a file, or delete anything.
It's also possible to create conditions on one or several elements. Conditions will define how the content should be displayed based on a set of rules.
Click on the thunderbolt to create a condition.
Give the condition a name.
Select what should be used as a critiera (contextual information such as weather information or your own datasources)