A menu is a set of links, displayed on your website.
Links can point to any part of your website, or to any external website (for example, your Twitter or Facebook page).
A menu is displayed within a Menu Component in your website design. There must therefore be a Menu Component in your design for each menu you wish to display. The position and style of the displayed menu is defined by the Menu Component in the design tool.
PhotoDeck base themes include a single menu. To add a new menu, you must both create a new menu (set of links) and the corresponding Menu Component in your design.