Anyone can add links to their forum posts (to webpages, images, files, etc. as long as at a valid web URL).
Any full URL (with http etc.) is automatically make a link when posting. To make a link from a valid full URL, select it and then select the text then click the globe icon (top left above the post editing window) which will enclose the selection with a 'url' tag in square brackets. Job done. But, if you want to use some text in your post as the anchor text there's an extra step. First, select the text then click the globe icon (top left above the post editing window) which will enclose the selection with a 'url' tag in square brackets - I can't show that here as the tags will work as actual tags. In the example below I'll use {} for []. We select 'some text'. After clicking the globe you get:
{url}some text{/url}
To add the target URL for the link, edit the opeing {url} tag adding a '=' and the URL to the opening tag:
{url=http://www.eastgate.com}some text{/url}
Done. Insert an image in you post, it must be online. Copy the URL of the image and past onto a blank line in your post. select the whole URL and click the picture icon (third from left above the edit box) and a pair of 'img' tags are added around the image URL. No further editing is needed. Tip: I find that to ensure some space above/below the image in the rendered post it is helpful to leave a blank line both above and below the image URL in the the source of your post.
Note this forum configuration does not allow the direct upload to files, images to be stored on the forum. If you don't have web space of your own, Dropbox allows you to give public read-only URLs to items in your Dropbox. I suspect the Apple iCloud allows the same (Not sure!).
I hope that helps.
Edited: Corrections!