Let me try to address some of them with this post. Please feel free to ask follow-up questions if I've not captured what you need help with.
To post a picture, it needs to be hosted somewhere on the web (we don't host pictures ourselves because we've had security issues as a result of doing so in the past).
The picture needs to have an address that ends with:
.gif
or
.jpg
or
.png
which are the acceptable image formats for the format.
Here's an example URL:
http://www.somesite.com/someimage.jpg
When you have that, just click the 'Img' button in the text editor, paste the URL, then click the 'Img' button again. Done!
As for hosting pictures, I currently use a site called photobucket--
http://www.photobucket.com
It's free, and when you upload your pictures, it gives you all the information you need to quickly post the pictures here! (just grab the URL).
Once you have that you can even put the pictures into your profile so it will show up next to your name. Just click "Profile" at the top of the page and edit as appropriate.
Hope this helps!
-a