Welcome Stephanie.
Elgin posted good links for you but to answer two of your questions directly on the orange bar at the top of the page are links. Click on the one that says "user cp". That is your user control panel where you can edit/modify/change your profile. You can also see your reputation points there. That's also where you can add an avatar. To post a picture go to the gray bar above the orange bar I previously mentioned. You would then click "picture galleries". You will upload your pic to the "who am I gallery". It may take awile for it to show up, all pictures have to be approved first before they're added. If you have anymore questions feel free to ask.