Work on a new design - while the old design is in use
If you want to work on a new design in the webshop, it can ONLY be done partially without affecting the active webshop.
You can make changes to design settings (colours, font, menu type, etc.) without it appearing immediately. This is done under "Appearance > Design". There you can add a new design next to the current design. You can work on the new design without using it in the webshop.
Changes to content (pages, items, menu links, etc.) will be visible in the webshop immediately.
If you want to work on new content (pages or items) that cannot be shown in the shop immediately, you can make the page or item non-public. When you are ready to make the change, you can activate the new pages and items while deactivating the old ones.
It can be beneficial to work on page sections on a non-public page. Once you're happy with the look and feel, you can copy each section to the pages where you want to display them.