I always recommend creating a new page within the Not Linked section. Just like the pages found in The Sandbox, this way of working allows you to build your page at your own pace without it being live on your site. 

When adding a new page:

• If you want to use that same structure of an existing page for new content, you can duplicate the page. Hover your mouse over the page you’d like to copy, and select the gear icon. Within the page that pops up (General), scroll down and you’ll see Duplicate Page. Confirm and rename the page to what you’d like it to be.

When creating a brand new page:

• In the Pages panel, click the + next to Not Linked. You can start from scratch with a Brand New Page or explore one of the many Squarespace templates.

Either way:

• Click the gear icon of your new page and toggle off Enable Page while you’re working on the page. When it’s ready to be live, toggle on Enable Page.

• Always check how everything looks in Mobile! Watch this tutorial for advice.