Before you create your menu for this theme, make sure your pages/sections have been created already. This way they will be available to be inserted into the menu. Also note that if you have imported demo content using the 1-click import feature of this theme, then the main menu will already be created for you and some of these steps will not be applicable.
Go to Appearance> Menus in the main admin menu.
At first you will probably need to add a menu, give it a name & click Create Menu. The new menu will appear in a tab in this location. Click on this tab to begin adding menu items.
Use the dialog boxes on the left hand side of the page to add items to your menu. Select the page you wish to add to the menu and click "Add to Menu".
If you wish to use submenus then firstly you must create a top level menu item. This item may not hold a link. Therefore to create this item you would use the "Custom Link" dialogue on the left side of this page, near the top. Simply enter a "#" character as the item url, and give the item a title. Then add it to the menu as you would do normally. Once its in the menu drag the sub menu items to be children items of this custom link item.
Now you can drag the newly inserted menu item to their correct sequence and rename their titles if required.
After you have added and edited the menu items click Save Menu in the bottom of this area.