How to post pics: When writing a message, scroll down and use the "attach file" option. Where possible, a photo sharing service can be used such as Flickr, Imgur etc. The image location (usually ending in .jpg) can be copy and pasted between the ][ brackets that appear when you click the 'Img' button (you can find this button at the top of the message box).
How to post youtube vids: Click on the 'youtubeHD' button at the top of the message box and in the middle of the ][ brackets that just appeared, copy and paste everything from the youtube web address that appears after the = sign i.e if this is the url: https://www.youtube.com/watch?v=K2cNqaPSHv0
just copy "K2cNqaPSHv0").