how do I run slideshow from flash drive
How do I run a slideshow on mac from flashdrive pictures?
Depends on what created the slide show. If it is just a bunch of pictures on the flash drive as individual files, you can select all, and use Quickview in the Finder. That would let you navigate the slide show with arrow keys.
Preview also allows you to open multiple files at once, and make a full screen slide show navigating with the arrow keys. It gets more complicated if the video is Windows Media or something else. What do you see that is on the flash drive?