Embedding a video means to put the HTML code for the video in your message,so the video will appear,rather than being a link to the video.
Here is an example of an embedded video,using the hosting site YouTube:
For whatever reason,Network54 will not allow you to upload videos directly to be hosted on its site (probably to save money,etc.)
So, you must host the video somewhere else on the Web. YouTube is a free hosting site.
See my FAQ for embedding videos from YouTube: