By default, Ubuntu goes into idle mode after 5 minutes when your computer not in use. Once it is idled, screensaver is immediately activated. This tutorial shows you how to change the time your computer goes into idle and also change when screensaver is activated. This article should help those who are new to Ubuntu and are still learning how Ubuntu works.
To get started, go to ‘Power –> System Settings’
Then select ‘Personal –> Screensaver’
Finally, select ‘Random’ Screensaver theme, then use the slider to specify when your computer goes into idle mode, and click ‘Activate Screensaver when computer is idle’