Select "File | Open..." menu item.
You are given a standard file open dialog.
Select the file you want to convert.
River Past Video Perspective supports a range of video files. The complete list supported formats can be found here.
Once River Past Video Perspective accepts the file, and display the first frame in its window.
Use the 
"Play", 
"Pause", 
"Stop", 
"Step Backward", 
"Step Forward" buttons, and 
slider to preview the video.
