An image tag inserts an image into your text. You cannot upload this from your computer, it has to be hosted on the web and have a URL. If you want to upload your own stuff you first have to publish it on the web using something like Photobucket. In any case a image tag looks like this BUT YOU MUST OMIT ALL SPACES
[ IMG ]http://WWW.yourimagegoeshere.com[ /IMG ]
A video tag is much the same. Again no spaces.
[ media ]http://YouTube.com/blahblahblah[ /media ]