Copy the Superfish module to sites/all/modules or sites/sitename/modules.
Copy the Libraries API module to sites/all/modules or sites/sitename/modules as you require.
Download the latest version of the Superfish library and extract it to sites/all/libraries or sites/sitename/libraries as you require. The extracted folder must be named superfish.
Enable Superfish and Libraries API modules.
Go to Administer > Menus > Primary links > Add link.
Check the 'Show as expanded' option for parent menu items only if you want main menu as drop down.
When you are done everything should look like this:
sites/all/modules/superfish (the Superfish module) sites/all/modules/libraries (the Libraries module) sites/all/libraries/superfish (the Superfish JavaScript)
Hooray! Now we are ready to configure some Superfish menus.