Where to begin?

I am doing this primarily for my sons.  There are so many things that will never be said between us, and I want them to know all of this--I want them to know me.  I don't know if I will even tell them of this while I'm alive, because I can be more honest if I don't think everyone I know will see this day by day.  I don't know.  I'm a big fan of Mark Twain, and his autobiography in particular.  He often speaks of the fact that he can be honest as he is speaking from beyond the grave.  This is something similar.