All you have to do copy the last part of the youtube url which is the code for that particular video, then write youtube on each side of it in brackets, with a dash before youtube on the second one. Quote holeout's imbedded post and you will see the format. For an image you write
That's the link to the video. Take the part after the = sign (i.e. v_aPnGqQkVg) and put it in between [youtube ] and [ /youtube] with no spaces. I put the spaces between the brackets and writing so that it would post.