I found yet another editor who was confused by the "Insert > Multimedia files" dialog in the VisualEditor, in particular by the "Upload" button.
See how it looked for her:
In truthness, when this dialog pops up there is no indication whatsoever of what might be the next step. One can only guess that clicking any of the images will do something meaningful, and that after clicking one of them you have to click the "Use this image" button which will appear in the top right. Instead, the interface suggests that there are two options, given by the two buttons: Cancel, or Upload.
What happened: the user uploaded files on Commons https://commons.wikimedia.org/wiki/Special:Contributions/MARTA_MANCINICons and had no idea how to insert them; I pointed her to the manual and told her to open https://it.wikipedia.org/w/index.php?title=Agide_Jacchia&veaction=edit , click Insert > File, search and pick the images ; she did so, she saw the images, but she clicked "Upload" and ended up trying to upload the images once again.
Possible solutions (not alternative to each other):
- remove the "Upload" button;
- move the "Upload" button in some place where it doesn't seem to be the next step;
- actually show the next step: display the "use this image" button even before an image is selected, but greyed out (maybe when a search result pops up, or even before a search term is entered);
- remove the "Upload" button when there are search results;
- make it visually clearer that the "Upload" button is not a button for the current action (searching an image to insert) but actually a different operation/tab which happens to be in the same dialog for some reason (currently, Search/Upload don't really look like tabs, so the aspect doesn't help even the users who are familiar with tabbed interfaces);
- add some text explaining what one is supposed to do [this is usually just a false solution].