Menu manager contains list of all menu items of website and allows options such as add,edit,rebuild menus. First you need to login on Joomla administrator panel and navigate to Menus> Menu Manager from the menu across the top of the Joomla administration screen.

New It is used for creating new menu.
Edit You can edit an existing menu using this option.
Delete You can delete a menu using this option.
Rebuild It refreshes the menu table.
Help It is used to provide help option.
Options The options can be set by you related to the page display and permission, like Browser Page Title, Page Heading, Page class, along with permissions of accessing options by various users of the site.

The process for creating a new menu and display it on the website is as follows.

Create a menu> Add menu items>Create a module for the menu>Select module position