From the Mouth of Teenagers

Who is Heavenly Father (God)?  What is He?  How do you know if He is real or not?  These questions have troubled many great minds and the simple ones (such as mine).  Obviously, I know what my own answers would be to these questions and could write a novel about them.  But, to shake things up a tad, I asked the youth (ages 12-18) from home to answer them for me.
First question, who and what is Heavenly Father?