Each time you click on a Template or create a new design, it begins a project file. Your designs are saved in a project file on the My Designs page which is located on the left side bar.
Additionally you can download (.PNG), duplicate, or delete designs to manage your workspace by clicking the ellipses menu which opens up more options. To see the ellipses on web, hover with your mouse.
To download on mobile, just tap on the design, go to Share (blue on the top right) then click Share again on the bottom.