If you mean the VIDEO_TS folder that has been copied/ripped from a video DVD and contains .vob, .ifo and .bup files, then VLC Player and Mac OS X's own DVD Player are capable of doing that by just dragging the VIDEO_TS folder onto the application icon in the Dock or the Applications folder, or by opening them via the applications' menu.
Also have a look at the following links, as the information presented there might be helpful in your future endeavours into Mac OS X and could clear up initial confusion and may even prevent harm to your system or your files.