How do I add a pic to my side profile on the msg board?

I feel really bad asking this, however; I'm still kind of new to this. I don't get much chance to frequent as often as I'd like. I love the support that everyone seems to offer here and I think I will try to make more of an effort to get on.
Can anyone explain how I can get a pic to go with the profile that shows up at the side whenever you post. I would appreciate any help. Thanks so much.