I have a page set up already which is /abax

I would like to create new pages for example abax/sub-page-1

In the page set up theres an option to select a page folder. I assumed this would give me the option of choosing an existing page as the parent page but the drop down is empty. Is there a way to easily accomplish this please?

You have to create the folder beforehand for it to be selectable, Steve, so you need to go back to the Pages menu, and then click "Add Folder", which you will call "abax".

After that, you'll create a page, calling it whatever you like. Once the page exists and you've assigned its location to that folder, toggle open the "abax" folder on the Pages menu, and any posts you've created there will be listed. Click the down caret for the relevant page, and you'll see an option to make it the folder's default. That's the page which will appear at yoursite.com/abax. Any other pages in the folder will be at yoursite.com/abax/pagename.

Thank you

Thanks, @Meddysong. 🙂