As @build-it.assist said, you can attach your video or the video you are sharing from the youtube in your post. Simply copy the youtube address of the video and past it in your contest post or general Build-It post. If you are writing the post for the contest entry and video is not you own then describe the details in your own words, as mentioned the CONTEST post as well...

Explain the procedure briefly, its benefits, and your point of view about it.

Thanks.