This page (reached by clicking on or hovering over your name on the top-of-page welcome message) lets you:
Click the "Edit Information" link (or the pencil icon) below the picture/image to edit your name, email address, password, and time zone information. It's also where you can upload a picture for this page and for document pages where you make comments. If you don't want to upload one then this default image will appear for you:
There's a separate "Bio" link that gives people some context information about you when they're reading your uploaded documents and comments; it's nice to know when a person commenting on astrophysics really is a rocket scientist!
The "Notifications" link takes you to a page where you can control which email notifications you get:
The "Privacy" link lets you control how much information about your Public Documents shows on your public Profile page.
Your Profile page also displays:

There's also an RSS link to let people find out about new Public Documents you upload:
Private Documents won't show on the RSS feed; only people you choose to share Private Documents with can access them.