What does this error mean?

what does this error mean?
Fatal error: Cannot redeclare host() (previously declared in /home/content/b/r/a/username/html/get.php:20) in /home/content/b/r/a/username/html/get.php on line 31

i tryied using session_start() and destroy
but nothing happend
any help?:D

is the session start before everything else in the file (before any html etc)?

You are declaring a function with the same twice or are including a file that defines it more tan once.