Add a File to the Media Library
To upload a file (jpg, png, pdf, doc, etc) navigate to the media and select the folder to which you want to add the file.
Most media folders are under Categorized > Libraries
Navigate to the section of the library in which you want to add media
Click the add media button on the top right above the media items
Add the file by dragging it into the media library, or by clicking the box and navigating to the file
Always put text into the description field. That field is used by screen readers for the visually imparied. Failing to include text in the description field is a violation of ADA policy.