After you file

I understand you competly i've lived in this state since 2015 and filed taxes here and i've Never had to do a D400 form, i have no idea what it is or why i need it, im honestly confused, because i am able to efile my FED now, but i dont wanna file and then have some issue with my State taxes. what exactly is this form, NO the website DOES NOT provide clarification on what this form is, NO, i do not understand it, and never seen it before.