You shouldn't have to do anything. It should already be set up that a pps
(PowerPoint Show) is opened by PowerPoint directly into the show. If not,
your file association is messed up. Just fix the file association.
If, OTOH, you mean how to get a pps file to open in the edit mode of
PowerPoint, just open PowerPoint and then open the pps file from within
PowerPoint. Otherwise, simply change the pps extension to ppt. Then, upon
opening, the file will invoke PowerPoint in the edit mode.