Login to your website and from the Dashboard, select Plugins and then select "Add New". Type "mega menu for wordpress" in the search box. A list of plugins will be displayed but this is the one you want.

Activate the plugin and once you do that you'll see the "WP MEGA MENU" tab added to your dashboard on the left hand side.

You can check out each of these settings but you can leave every thing as is under the "General Settings" and "Theme Settings" tabs.

Let's go to the next page to create a new menu to work with.