Hypertext Markup Language.
Use <img src="Image source directlink" title="Mouseover text" /> for images, links:
<a href="Link here with http://" title="Mouseover text here"> Clickable text here </a>
You can make a left-to-right line across the post with <hr />

Um yes there's a lot more tags but a few tags that aren't deemed suitable for posting in user content (scripts, CSS et al) have been blocked, so you'll just have to experiment. A few safe bets are obviously all presentational elements such as bold, italic, monospace, code blocks and some table things.

1. You upload your image to the Internet via image hosts. Some of the best are Imageshack and Tinypic. (Tinypic erases yours after some time, so no liek)
2. You get the picture's link via "share image" or "copy link" etc
3. You paste the link to the src=" link here" part
4. ???
5. PROFIT!
OR
there is the harder and more vulnerable method.
1. You make a DNS Redirect URL for yourself
2. You access the router and port forward
3. You post image directlinks that this time are totally direct.
By the way. If you don't know anything, use Google. www.google.com
For a tutorial on using imageshack, search with Google.
For other HTML shizz, search with Google.
Etc.