hopefully this helps and is not too confusing.
If the image is online somewhere - you need to either type this, or click on the little image icon (second icon from the left) and the (img)(/img) text will come automatically.
(img)http://www.imageurl.com(/img)
it will will give

replace the round brackets with square ones and you are in business. To find the image location, right click on the image and select 'copy image location' then come back to the forum and PASTE it into where you want it.
To make the image so that it is also also a link - it is a little more tricky.
(url=http://www.linkurl.com)(img)http://www.imageurl.com(/img)(/url)

and again replace the round brackets with square ones. Notice that the link url is INSIDE the brackets with an equals sign.
And lastly, if you want to just attach an image you have on your hard drive somewhere.. you need to click on 'additional options' - which is just below the typing area, and then browse and find your image on your hard drive - then click post.