The first thing that you have to do is upload your photos to the web. You have a couple of options here.
The most popular is to use an online gallery site like http://www.pbase.com or http://www.smugmug.com . Once on the site, then right click on the picture, select properties and "copy" the image location. Creat a new thread and "paste" the image location in it. Click "Preview" to ensure that the link is correct and post the image. There are also a few free photo hosting sites, but as luck would have it, I have no idea what they may be.
Or, if you happen to have your own web site, just upload the images to your site and paste the location in your thread.
Just try to remember to make sure your photos are in sRGB colour space and resize them to a width of around 800.