can't exclude categories from home page

I want to limit the posts that show at the bottom of the home page to only a certain category. When I try to add a line of coding to the home.php to do this it either gives an error message that says the code is interrupted or it just displays that category page instead of the home page.

I would also like to add coding that limited the number of posts that display. I imagine though if the way I have been trying to alter the category that displays isn’t working that wouldn’t work either.