Once you've customized a template or created a design from scratch, you can save it using the 'Save' option in the editor. You will find this at the blue top bar, next to the 'Resize' button.
Once you’ve saved a design, it can be accessed from your My Stuff page, from where you can edit it again or download it, publish it on social media, add collaborators to it, or create duplicates.
Save a design via your mobile phone
You can also save your designs when working from your mobile phone.
Click on the icon on the top right side of the screen. This will save the design.
For further reads, read this article to learn how to get a free download.