Menu
Go to Admin -> Appearance -> Menus.
Flow has one menu with a display location, and a menu that you attach to a widget. Both are managed on the same screen.

To change a menu, click Edit on its row. Add pages, categories, tags or custom links from the boxes on the left, drag the items to reorder them or to nest them as submenus, then save.
Main menu
The main navigation of the header. Its display location is Main Navigation (box Menu settings at the bottom of the menu editor); it is the only location of the theme. The demo menu has Home with the 3 home layouts as submenus, Galleries, Blog layouts (the 5 blog pages), Post layouts (the 3 post title layouts) and Contact.


Go to Admin -> Appearance -> Menus and edit "Main menu".

Quick links
The Quick links menu has no display location. It is shown in the footer by a Custom Menu widget of the Footer sidebar 2 area.

Go to Admin -> Appearance -> Menus and edit "Quick links".

To change which menu a footer column shows, or its title, open Admin -> Appearance -> Widgets. See Widgets.
Menus in another language
Each menu can be translated. Open the menu and use the Languages box on the right to switch to the other language. See Translate.