“Call to undefined function” message

I’m very new at this, and there is probably some simple explanation, but when I tried to open the install.php file (after creating the wp-config file and all of the other steps) I recieve this error message:

Fatal error: Call to undefined function: is_wp_error() in /home/jared2/public_html/wordpress/wp-includes/functions.php on line 1320

What does it mean?

Thanks!