Who am I

How do you answer the "Tell us about yourself" or "Describe yourself" question? I never know what to say.  I want to be honest & confident but not boastful.  I want to answer the question like it were asking "who are you?" but I struggle. The things that I write are not really who I am, but who I am in relation to other people or what I do.  I can't say what i do because that is a separate question... "what are your hobbies?" I cant start off with, "I am 21 years old..." because I have probably already put my birth date down. So what do i say?
I guess I will just stick to what I am good at...

I am Brittany Hellmeister.  I am 21 years old.  I am a mother to a lovely little girl and the fiancee to the most amazingly amazing man. I love Reese's, sports, and the internet.  I have two serious addictions: Celine Dion and chap-stick.