Help me!

[Massiel]

Every time I try to add a new hack, no matter how simple it is, I get errors. I don't know much about php so I am a bit lost. I know my explanation is vague but I don't know how to be more clear. I tried installing the random smilie hack today, it was a simple change. After I uploaded it the site went down and I got a error msg on the admin/functions.php

Any ideas?