Click the Go button, top-left, select "personal zone" > Profile. Once there, click "View/Edit... top-right. From there click to add a photo (avatar). In the next window, click "Custom Avatar" and upload your photo.
When you block a person, they can no longer invite you to a private message or post to your profile wall. Replies and comments they make will be collapsed/hidden by default. Finally, you'll never receive email notifications about content they create or likes they designate for your content.
Note: if you proceed, you will no longer be following .