Thumbnail pix

I saw a post with very nice thumbnail photos with a black backround that I was able to scroll through. I would like to post some pix of my grow room in this fasion. How do I do this?

I already have the pix uploaded into an album on this site.

Thank you very much for your help

-G4P

Example
https://www.rollitup.org/grow-room-design-setup/191151-how-hook-up-fan-cool.html

Go advanced and click on the paperclip.