To manage Menus go to the Menu.
Menu group is a selection of menu items. To create a menu group, go to the Menu/Add Menu Group. Give it a name and caption and save it. Now, you can add menu for that menu group.
Main Menu for website language(s)
If you want to have a menu group as main menu for a language, select language(s) in Default Language section, when you are creating a menu group.
Menu is referring to menu item inside a menu group. To create a menu, go to the Menu/Add Menu. Select the menu group that you want to put menu item in it. If menu item is sub item of another menu item, you can select parent node in Belongs to section.
You can also add HTML content for a menu item. Theme can show that content inside a menu item.
Options
Important: If you mark a menu as important, That menu will be shown as bold (Depends on theme).
Show Description: If you mark a menu as show description, The description content will be shown inside a menu item.
Add Free Space: Theme gives the menu item a little bit more space (Split size between menu items will be more than normal).
Publishing
In the Publishing tab, you can specify Date From and Date To.
If you only set a date and time for Date From, It means the menu item will be available from that date and time forever.
If you only set a date and time for Date To, It means the menu item will be available until that date and time.
If you set date and time for Date From and Date To, It means the menu item will be available in that period of date and time.