Right-click the desktop and choose “Enter Edit Mode”. Then right-click the desktop again and choose “Configure Desktop and Wallpaper”.
You will right away see a setting called “Layout:”, which is set to Desktop. Change that to Folder View and click Apply. It should now show you the contents of the ~/Desktop folder. If it doesn’t, or if it shows another folder, click on “Location” in the column on the left and change it to whatever you wish.
When you’re done, click OK. Don’t forget to then also right-click the desktop again and choose “Exit Edit Mode”, so that you don’t accidentally move or remove widgets.
P.S.: I do not believe that Plasma has a Computer icon ─ that’s a Microsoft thing. It does however have a Trashcan icon.