There are THREE areas to fill in, the "Required Information", the "Additional Information (Optional)", and "I am on this website because (Optional)"). Â
You are only required to fill in the first section (Required Information), but I really encourage you to fill in all items in all three categories if you want others to find you when they do an ADVANCED MEMBER SEARCH.
One of the options in Advanced Member Search is to search by keyword, so if, for example you love movies, and someone is searching for members with "movies" in their profile, they will find you.
You complete your profile by logging in and going to "My Stuff" -> "Edit Profile"