If you don't understand them, it means you don't have the problem they are solving - a lot of UI components open all at once.
But whenever you're overloaded with multitude of items, grouping may help you. And sometimes you can distinguish some non-overlapping groups of GUI components. These are activities.
Like: For staying up to date with life (my eMail client, my facebook page), for the project I am currently working on (my IDE, some folders of the project I am currently editing, GIThub page, various googling sessions I am doing in research), for the entertainment (my favorite offtopic sites, etc.).