Firstly, you need to registered for this site.
You can’t upload video directly to this site. Video file sizes and video streaming require specialist platforms.
You need to host your video on either, Youtube or Vimeo. These accounts are free to set up. Youtube is part of Google so if you have a google account login then you can upload video to Youtube. If not create one.
Once uploaded you will be able to copy the video URL:
Once you have copied the URL you can then Submit a Post on this site and add the copied URL into the form as shown below.
Vimeo is very similar and has a share button on each video which allows you to copy the video URL