To put a video directly into the post instead of just linking, find the
Video button(On the same row as the Font\Bold\Quote buttons). Copy the
link of the video you want to use, paste it there and hit OK. Note, when
copying a link from Youtube, you must copy the link from the actual
video page, not from the video on the users channel. The final video
code on your post may end up on the very bottom, to avoid this use the
Switch to Editor Mode option (a/A).