1.  The image want to put into your forum post will have to be stored on a web-site somewhere, you can add this to the club site see HERE or a free photograph hosting site like www.flickr.com
2. Once you have uploaded your picture you need an HTTP link to the image, this will be of the form www.mywebpage.com/myimage/myimage01.jpg. You can often get a link to the image by clicking on the right hand mouse button when the cursor is over the image, this will display a menu. See HERE for more details on how to do this.
3. Once you have this you are ready to add the image to your forum post. You can click on the  'Image' Icon or type the text into your post directly, either way the link to your image needs to be placed in text between [img] [/img] tags like so.

[img]http://www.mywebpage.com/myimage/myimage01.jpg[/img]