Go to footytube.com or whatever, and get the embeddable url from the video: there is usually a share button you can click on and it will pop up the url. Copy and paste that url into the embed video section of your upload. You will have to edit the video width and height tags in the url itself. Usually it is set to undefined when you copy it. If you don't do this the video won't show up.
Noob question here but how do you embed a video within an article that you are posting?