EventTrigger is required to start storyboards when a surface event has occurred. Mostly these are mouse, keyboard or pen events .
To do this, open the trigger window (click on the triangle in the top right corner). In the trigger window, press the "Event" key (1) . Then select the event in the "Trigger data" tab at which the storyboard should be started (2) :
Close the trigger window and switch to the XAML editor. An EventTrigger was added to a Triggers list. Here's an example:
Then you have to insert the section with <BeginStoryboard> yourself by copying the XAML code for the storyboard from Blend using "cut-and-paste".