Hi Sandra,
The URL alias is just to give your article alternate name of getting to it. If you put "my-orchid-article" in the alternate URL then you will be able to get to it by going to
www.orchidboard.com/my-orchid-article that's all. This will also help out greatly with Search Engine Optimization (SEO). Properly named article will get much more hits from engines.
As far as formatting your article, you will probably find this useful, tells you about the image tag also
http://www.orchidboard.com/community/misc.php?do=bbcode
You can edit your articles by the way.
btw, if you need help with layout, picture resizing, let me know and I'll help you out.... in fact, I reserve the right to edit your posts if the layout will be off