あなた go to YouTube go to a vid u like and look where it says ADRESS または WWW.YOUTUBE.COM.and click your left button.if あなた did it right it will say cut copy paste.if it doesnt click the other button.always copy.then paste.
well, the way i do it is first go to YouTube (it doesn't seem that あなた can do this with other websites) find a video あなた like there. then under the vid it should have a button that says share click it then it should have a highlighted bunch of letters right click it then copy then click 'embed a video' back here and paste. simple.
here's a ランダム vid that i embed just to 表示する it works.