As a page builder you choose the type of page you want to build when you create a page. Read more about the types of page you can create.
You can make changes to a draft copy of the page, and then publish it when you're ready.
Once you publish your page, you can access designer mode at any time to edit and customize it further. Click the pencil icon in the top-right of the page to enter designer mode.
If you want to use a page as a starting point for another page, you can duplicate a page.
You can also move a page to another app, or delete a page.