You will need 10 posts before you can post a pic or upload an avatar (profile pic). Once you've reached 10 posts, go to your profile(link is in blue bar above your username "logged in as"), then click on the "personality" link on that page. You'll see where to go from there.
For Avatar help https://www.backyardchickens.com/forum/viewtopic.php?pid=8134#p8134
For photo help https://www.backyardchickens.com/forum/viewtopic.php?id=504
For Avatar help https://www.backyardchickens.com/forum/viewtopic.php?pid=8134#p8134
For photo help https://www.backyardchickens.com/forum/viewtopic.php?id=504