The desktop toolbox, accessed via the upper left corner has a button for displaying your activities, of which Plasma™ allows you to have more than one. Basically, that is multiple desktop containments hosting multiple sets of Plasma™ widgets. Display the “Activities” bar, select one of the predefined activities or choose Create Activity to create a new containment, select your new containment and customize suiting your taste. Plasma™’s activities and KWin’s desktop grid are similar in that respect, but there is a fundamental difference. While virtual desktop are used to group and organize windows, Plasma™’s activities are used to group and organize Plasma™ widgets. This way, you can switch between activities and have relevant Plasma™ widgets supporting the task you are currently trying to accomplish. You can create a “Free time” activity, with comic strips, a puzzle and other Plasma™ widgets, and a “Work” activity, with relevant RSS feeds, calculator and calendar, for example.
To delete an activity, press the button on “Activities” bar (press Alt+D then Alt+A to open this bar) then click the red 'X' (or press Alt+D then Alt+R) and confirm the deletion.