Moodle for mobile
Moodle can be used on a mobile device by downloading a native app, such as the official Moodle Mobile app. See Mobile Moodle FAQ for links to more mobile apps.
Moodle's standard theme, Clean, is a responsive, bootstrap-based theme, meaning it will adapt well to mobile devices.
An administrator can also set a theme for mobile devices in Administration > Site administration > Appearance > Themes > Theme selector. The Simple theme is multi device optimized. The Standard fluid theme is a good start if you like to code your own responsive web design theme in Moodle, or if you use the 'standard' theme and would like to make it ready for smartphones and tablets.