An SWF file (Small Web Format) is a container for playing back FLV (Flash Video) files---a popular type of streaming video on sites like YouTube. These files are recognised by VLC Media Player and can be opened just like any other file supported by VLC. If you cannot open an SWF, try downloading the latest version of the program, in case your current version is corrupt.
Click the "Media" tab at the top of the screen and select "Open File..." to enter a pop-up "Open..." window.
Browse your hard drive's contents for the input SWF file and highlight its icon. Click "Open" to load its contents in a new VLC player window.
You may also open files by dragging and dropping their icons from your desktop or computer directly into the empty VLC Media Player window.