Choosing a screen name can be very important for any site. Screen names are often written in stone so to speak (or the database, in reality), so they are not easily changed. A screen name or log~in name must be unique for every user of a site. That means that if 2 people have the same first name and they both want to use their first name, then only the original user will get to choose that name.
This also brings up another good point, sometimes people want to use their real name and sometimes they want to make up a name or use a nick name. If you want to remain anonymous, then you should chose a screen name or username that is cute or funny (but not vulgar). Something like SkinnyMe or TheNewMe. Names like this will allow you to be more open without worrying about the wrong person reading your post and judging you. Whatever name you pick, we’re glad to have you on board!