Yes, if a functions file exists, you would copy and past it there, anywhere before the closing php tag if there is one at the end of the functions file. You should see bunches of code in your functions.php file so you do not want to break up any group of code, just like the group above needs to be together with itself as he wrote it.
IF you do not have a functions.php file in your child theme, you can create one. Read up here to learn more. https://codex.wordpress.org/Functions_File_Explained
