I am new at this. Rember to consder this.
first thing you want to do is post a picture or an idea of what your trying to do. 
Don’t be rude.
(1) Find someone who will host your image online, like photobucket or imageshack.
(2) Use their service to upload your image. You’ll get back a URL which is your image’s address.
(3) When you Post a reply type something like
hello, this is my image. be nice. please help. etc.
The stuff you put between the [img] and [/img] tags is the URL you get in step 2.
Hope this helps.
Duoas - I wasn’t being rude, you just read it that way.
Choren - You can also upload your images to elYsiun’s site, though you only get so much space. (500mb?)
Yes, I did. 
Sorry. I shouldn’t have.
The upload to elysiun is pretty cool. Down at the bottom of your Post a reply screen you’ll see the Add an Attachment stuff.
My eyes are colored. (I’ve had a rough day, and the prospect of cramming all night for an exam tomorrow.)