This is a item. This is the main body of your website.

To edit the content here: Goto > Content Items Manager > Frontpage item

With Joomla, to create a new "page", is to create a new ITEM

To create a new item > Content Items Manager > New (top right button)

Once you have created your new Item ("page"), then you need to link it to your menu so that your visitors can view it.

When you edit a item, you will find tabs on the right-hand side, goto > Link to Menu > mainmenu > enter a name > Link to menu

Now save or apply the item.

Go back to your home page tab and refresh the page to see the new menu link