I was always fond of Bing Crosby's "I'll be home for Christmas" buy don't know how to post it here.
Open the video and click "Share" below the display. A screen will pop up with a number of aps, below that is a line with a web address. Click on "copy". You have saved the link to the video, you really don't need the YouTube screen anymore.
Returning here, click on the media tab, it's between the smiley face and quotation marks directly above the message text area. A box will open up, click on the empty box that says "Enter media URL", then right click on your mouse and select "paste". Then click on "continue" and it'll take you back the the main post entry screen and display a code for your video. Either before it, or after it add anything you wand to be displayed on the screen at the same time. After that, it's just another post here.