You may include links to other pages by just including the URL of the page in the body of your text. Be sure to include the "http://" and the URL will usually end with ".html" or ".htm". There is also a "Optional Link URL:" field at the bottom of the message entry page for including the URL along with a title. This will create a link at the bottom of the post. Again, remember to have the link start with "http://" along with all the other address information.
You may include pictures with your messages by including the address of the picture in the field where it says "Optional Image URL:". Note that only certain kinds of files will work here. The file needs to be a graphic file recognized by the browser. These are usually either "Jpeg" or "Gif" files and should end with ".jpeg", ".jpg", or ".gif". If you are uncertain use the "Preview Message" button to check before you post it. There are several other graphics formats which may work, but test to make sure.
The most common mistake is to attempt to link to the page which contains a picture instead of linking to the picture itself. This will not work right. If what you want to include contains a lot of text and stuff other than just the picture, you need to get the address of just the picture. To do this find the picture you want and right click on it (Mac users - click and hold). You should get a menu including something to the effect of "Open Image in New Window". Selecting this will give you a new window with just the picture in it. Go to the address bar of your browser which shows the current address of what you are looking at. Copy the contents of the address bar and paste it into the "Optional Image URL:" field in the message posting window.
If you are having trouble, try using the "Optional Link URL:" to provide a link to your picture instead. This should be less touchy. The picture won't appear on the message but at least people should be able to get to it fairly easily.
Never assume that your message will look the way you expect it to look! Previewing your message before you post it is always a good idea, anyway, but is even more important if you're using the above codes, since if you mis-type something, the message won't look the way you expect it to look!