XF 1.1 Adding custom HTML/PHP

hey guys,
i'm new to xenforo, but i wanted to add some custom html and php to some of my pages. i added the code through FTP but it never showed up on the page. am i doing something wrong?

i've tried adding code to both the admin page and the regular forum page and neither worked.

thanks in advance for the help!
i was trying to add the code to the admin control panel page which is located at /forum/admin.php for me. also wanted to add code to the main home page with is /forum/index.php.
well i have tried a few things with no luck. i tried debugging mode which for some reason only seems to change the page content when i intentionally make an error. for example if i leave a semicolon off then an error message is displayed. if i type something like echo "testing!!"; the changes won't show up at all.

i also tried the callback method that was suggested, but my xenforo version is 1.1.5 and from what i read the callback only works for 1.2

any other suggestions? i don't get why it's so difficult to edit html and css through an FTP log in...