Call to undefined function get_header() in wp

Hello,

i am using this code to going to page in my directory
theme there is ch folder

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    but going to page url wp-content/themes/live/ch/bn1.php showing this message

    Fatal error: Call to undefined function get_header() in C:\wamp\www\blog\wp-content\themes\live stream\ch\bn1.php on line 1