inc/special/upload.php
Used by the Special:Upload page. As this is used often, it is also directly in the edit menu.
Upload provides a form to upload a file to the site/files folder and creates an image page for it. You can upload any type of file you want. The max size is 8 MB. The upload uses standard PHP upload, so it is neither fast nor gives it a feedback on the progress.
You can name the file. If you don't, the filename will be used directly.
There is no revisioning for files. Uploaded files delete existant files if the delete existing files checkbox is checked. If not, numbers will be added to the file to create an unique filename.
You can then access the files using the Image link (for jpg, png, gif) or the media link (for all).