If this option is checked, tooltips are displayed hovering items in the Plasma panel or on the desktop.

If you change e.g. brightness and volume using the keyboard these status changes are displayed in an OSD.

This is the default setting. Clicking once on an icon will open it. To select you can drag around the icon(s) or Ctrl+Right click, or simply click and hold to drag it.

If this option is not checked, icons/files will be opened with a single click of the left mouse-button. This default behavior is consistent with what you would expect when you click links in most web browsers. If checked however, icons/files will be opened with a double click, while a single click will only select the icon or file. This is the behavior you may know from other desktops or operating systems.