On YouTube, you will see a 'Share' button below the video that you want to embed. Click that and you will be presented with a link to the video - copy that. When making your post here on CC, you will see a row of icons at the top of the edit box. The 3rd from the right looks like a piece of film - click that and paste the YouTube link in to the box that pops up, then click the 'Insert' button.