2 ways

1) the easy way:

Paste in the URL that you get from youtube or vimeo, etc.

it will look something like this:

“https://www.youtube.com/watch?v=5Dna1tkY8UA”
(without the quotation marks)

the video will automatically embed itself and look like this:

https://www.youtube.com/watch?v=5Dna1tkY8UA

2) the harder way
Switch to TEXT mode (top right)

and paste in the EMBED code that you get from youtube or vimeo, etc.

it will look something like this:

<iframe src=”http://www.youtube.com/embed/5Dna1tkY8UA?rel=0″ height=”360″ width=”480″ allowfullscreen=”” frameborder=”0″></iframe>