YouTube:

copy the ID tag or the complete URL
and put between tags

original URL: YouTube - Funny kitten can't jump
tag: fBA_lxUiwSg

soundcloud

Here's how you embed a soundcloud audio file.
You take the full URL of the soundcloud page (be sure you're not in the "stream" page but on the actual song or piece of audio).
like this: If you use https make sure you type http or it won't work.

Then paste this inbetween the SOUNDCLOUD brackets, or choose the little soundcloud icon (when using "advanced" options when you write your post).

here's the result:


VIMEO

Copy the url of the Vimeo movie you want to embed:
Then take that last piece of code 110771579 and paste it inbetween VIMEO brackets (or hit the little Vimeo icon when in advanced mode while posting)
Here's the result:

As always, if you have some trouble with embedding links, don't hesitate to contact a moderator please?