Hello @kartik,
Include the first file into the second that's it.
See an example below,
File1.php :
<?php
  function first($int, $string){ //function parameters, two variables.
    return $string;  //returns the second argument passed into the function
  }
?>
Now Using include to include the File1.php to make its content available for use in the second file:
File2.php :
<?php
  include 'File1.php';
  echo first(1,"Hello edureka"); 
?>
Hope it helps!!
ThanK you!!