 To control themes, logged in as an administrator via the front page, go to the settings block, side administration, appearance, themes, theme settings. These are the global theme settings. You may decide to allow user course and or category themes. Allow theme change on URL may be very useful for session themes and or mobile devices. Custom menus become very trivial if you follow the syntax on the theme settings page. Save your changes when you're done there. Go to the theme selector. You can see here an array of themes that essentially vary by color, font and layout. The administrator can choose their preferred theme by simply selecting the button to the side of the theme, either for modern or old browsers. Some themes also have some settings that are directly accessible via the Moodle administrator interface without requiring server level or FTP access to control certain settings such as logos, link colors and custom CS and the like.