For starters, sign up with an image uploading/sharing site. For this example, I use
www.imgur.com as it is recommended fastest access of photos in North America, South America, and Europe and Asia. Second of all, for your avatar, it must be 100 x 100 pixels dimension, if you resize and/or crop some image. Then upload that image to that photo sharing site, a public or private album, and get the url towards linking it. Imgur has built-in copy ability for our board either in direct link or for images we post here in topics.