Duplicating elements allows you to quickly build out multiple versions of the same customization styles you have already done and that need just slight changes, saving you of creating new elements from scratch.
How to duplicate Pages or Graphics
A) For Pages: Go to Engage > Pages
B) For Graphics: Go to Engage > Graphics
(1) Click on the 3 dots over the element you want to duplicate
You should see a drop down menu appear.
(2) Select the Duplicate option
A copy of your elements should appear on the same Experience.