Functions.php won't work in child theme!

Hi, I have made a child theme for Catch Box on my site and have added header.php and 404.php inside it and they are working perfectly! However I want to add functions.php inside aswell as I have added a few functions to the file however when I added the file with all the content from the parent theme along with my custom functions but it ended up with a HTTP 500 Internal Server Error so I took a different approach as I had heard online which was to make the functions.php file and enter only the custom functions in it but the functions code just displayed at the top of the page! I'm not sure what else to do. Can someone help? Thanks in advance!