There are a couple of ways. The forum uploader is a bit picky. The image needs to be no bigger than 1500px across and I think it needs to be less than 1mb. I personally upload to Imgur, which generates a ‘BBcode’ for these forums. You paste that code in and it hot links the images. You can upload them pretty much anywhere, then copy the link address and paste it in your post, the add (img) before it and (/img) behind it, but use the square brackets —-> [] and the image will appear. This site is a bit of an old internet relic in some ways, so the functionality is a bit different.