Hello and welcome.
That looks like you inadvertently dragged hundreds/thousands of documents to the Desktop folder. Not sure where they all came from.
The easiest way to fix it is as follows:
-Open a new Finder window from the menu bar
-Click Desktop in the list on the left
-Click the button with four horizontal lines (List View)
-Press Command-Shift-N keys to create a new folder on the Desktop - it will be called untitled folder
-Click Date Modified to sort the contents of the window, and put the untitled folder on top of the list
-Start selecting and dragging all the files/folders on the Desktop list into the folder you created. Or, press Command-A to select all the files, then Press the Command key and click on untitled folder to unselect it, then click and drag on the highlighted/selected files and drag them into the untitled folder all at once.
It may take a while, but slowly the Desktop will clear. You can then go through the files/folders and reorganize them.
Do you happen to have a Time Machine or other backup of your data?
C
