Need to Make Sticky Posts Display Whole Post on Home Page

I need to display the entire post for Sticky Posts on on main/front/home page using WordPress and a Presswork-Child theme.
Any time I attempt to bring the functions.php into my child theme my page doesn’t load.
I have seen on many sites codes to either lengthen the excerpt/summary (I want to bring it up to 90 or so words) or, more ideally, to keep excerpts/summaries at 55 words, but to display entire posts when they are sticky. I am very unclear though if I should be creating a functions.php, loop.php, header.php in my Presswork-Child folder, whether this should include the entire copy and pasted coded PLUS the code to make (sticky) excerts longer, where this would even GO in the whole code, or if I should create a functions.php in my Presswork-Child folder with ONLY this one small code (thinking maybe all the rest of the stuff would just get carried over from Presswork)?
As you can guess I’m a real newbie at this, but hope someone can help.
Thanks,
Sofia