Avatar: Click "profile" toward the top of your screen, click "forum profile information" on the left sidebar, select, "I have my own pic" and paste the URL of the picture you want in the text box.
Youtube: Just copy and paste the url of the video. It has to be the full URL (not youtu.be) and "http://," not "https://" (Just delete the "s" from "https" to make it work.
PM me if you have more questions because posts tend to get lost among spam in this section.