First, find a Youtube video, for this example we'll use "Penis Enlargement Possibilities"
You'll see on the right a box with some html labeled "embed" if you don't see this box, click on "More info" - sometimes embed is hidden by default. I've marked it out for you in this picture.
By clicking on the code in the embed field, your browser automatically selects all of the code/text that you'll need to successfully embed the video. There is no need to manually highlight it. Right click and select copy or press ctrl + "c" to capture/copy the text.
Next, position your cursor in a Killoggs post/journal/comment box. Right click and select paste or use the ctrl + "v" hotkey. It ought to look like this.