Today I have added youtube video clip into my casualzone blog. It is as easy as ABC. It can be done in a second. How did I make it? Haha, you could follow google official website that teach you step by step to make it --> Link.
Basically you need to copy the embedded code (Embed) from youtube video clips that you want to add in. After that just paste the code into html- make sure you do this in edit-html tab (shown in the figure below). The embeded code is the highlighted one.