Hi Annie! I am a complete Luddite, but I'll answer as I think your post fell into the graveyard shift chasm:
You need to get your video onto the web first. Youtube is the most popular place to do this, so that's where I would start. It will probably be a bit tedious the first time (involving registering there, yada yada), but cannot be difficult as all sorts of morons have posted stuff there
To post on THIS thread, simply post the URL from Youtube. That's it.