It's nothing secret at all. A 2 second Google search teaches a person more than one needs here.
you were failing at it at the beginning of this thread
so here, for everyone who wants to know:
what people ARE messing up is the editor. If fancy GUI editor is ON then you need to put code using the video embed. Otherwise turning off fancy editor enables you to just write it in the text box.
for instance, to make large text one could use
<h1>big text!</h1>
which makes:
big text!
any site will give a good basic list of these codes
for example
http://www.web-source.net/html_codes_chart.htm
just don't annoy people with it.