You either go to 'manage attachments' and attach them as files, or host the pictures somewhere and link to them using the [img][/img] tags -
Ie -
using img ^^
http://www.willow.orcon.net.nz/wc%20unit/block.jpg
direct link.
Have fun
(yes, my block is ugly, its a testing model - i thought id keep it on topic though)