Step 1:

Click "Manage pages" in the upper main menu.

Step 2:

Here you can manage "existing pages", or add "new pages" by clicking "+ADD NEW PAGE".

To edit existing pages click on the "Edit" symbol (Pencil).

How to add newly created pages to your menu.

Step 1:

Click "Settings" in the upper main menu and choose "Menu".

Step 2:

Click on "Items".

Step 3:

In the box on the left, choose the page and "Add to menu". 

Step 4:

Arrange the menu item in which order you prefer, in the box to the right by dragging them.