This is exactly my question how do you put on attachments?
When you create a new post, there is an option below the text box that says "Additional Options..." Click on it, and it will display a couple of checkboxes, and an Attach: dialogue. Browse to the file you want, click open, and post your comment to see the attachment =)
http://forum.twilightonalex.com/index.php?action=help;page=post#attachments
The "Help" option on the menubar above will explain all of the basics with the forum. For the added features that need explanation Ive posted how-to's somewhere around either in the Fixes and Changes (http://forum.twilightonalex.com/index.php?board=24.0) board or elsewhere.