How do I make PNG files appear over a video? VEGAS PRO 17

I use VEGAS PRO 17. When I add PNG image files to my timeline the transparent background always appears black. How do I make a PNG image file appear over a video on my timeline?

I’m struggling to find any connection with your enquiry and any BorisFX product. Perhaps it would be useful for you to post your question on Vegas Pro’s forum -

Thank you