HOW TO ADD A VIDEO
If you want to post a video from youtube:
In the description of the video, you have the option "Share", in there go to "Insert". Copy and paste that code in the message field of your post, then, select all the code and go to Embed(at the top of your message) > Embed tags.
When go finish your post, you have to refresh the page if you want to see if it is working.