For people who have disabilities or are otherwise unsteady with the mouse, I usually suggest simply dragging (or saving in the first place the file to the desktop, then opening the target window and dragging it into there. Slightly more work, but very safe.
You can also use the default copy/paste system if you prefer, but the "original" will need to be trashed afterwards. There are a few programs available that act as a holding station as well. One moves the file to the holding point, then opens the target destination window and moves it the file again.
Do not give in to the temptation to keep everything on the desktop. The desktop is fine for temporary storage of things, but not workable for long-term storage for a variety of reasons.